Effects of sonication and ultraviolet-C treatment as a hurdle concept on quality attributes of Chokanan mango ( Mangifera indica L.) juice

Abstract

The growing demand for fresh-like food products has encouraged the development of hurdle technology of non-thermal processing. In this study, freshly squeezed Chokanan mango juice was treated by paired combinations of sonication (for 15 and 30 min at 25 ℃, 40 kHz frequency) and UV-C treatment (for 15 and 30 min at 25 ℃). Selected physicochemical properties, antioxidant activities, microbial inactivation and other quality parameters of combined treated juice were compared to conventional thermal treatment (at 90 ℃ for 60 s). After thermal and combined treatment, no significant changes occurred in physicochemical properties. A significant increase in extractability of carotenoids (15%), polyphenols (37%), flavonoids (35%) and enhancement in antioxidant capacity was observed after combined treatment. Thermal and combined treatment exhibited significant reduction in microbial load. Results obtained support the use of sonication and UV-C in a hurdle technology to improve the quality of Chokanan mango juice along with safety standards.

Keywords

Sonication ultraviolet treatment thermal treatment Chokanan mango juice antioxidant activity

Introduction

Mango (Mangifera indica L.) is a tropical fruit grown in 85 countries, ranking fifth in global production among other major fruit crops including bananas, citruses, grapes and apples. Mango production in Asia has increased about 15% from 2009 to 2011, contributing approximately 30.2 million metric tons to the international commodity market (FAOSTAT, 2013). In Malaysia, commercialisation of domestic mango cultivars especially Chokanan has reached the worldwide market as they are exported to Singapore, Brunei and Hong Kong. According to Spreer et al. (2009), there is a large stock of Chokanan mango yearly due to its ability to bear fruit even during rainy season. Thus, the market for value-added mango products such as juice, puree and nectar has progressively grown due to its perishable nature.

According to a study conducted by Rivera and Cabornida (2008), fruit juices have the highest acceptability among other beverages, generally due to their natural taste, as well as to the nutritional value associated with them. Consumption of mango juice has been linked to prevention of cancer, owing to its antioxidant properties (Block et al., 1992). Currently, thermal pasteurisation is the preferred technology used to achieve microbial inactivation and prolong the shelf life of juices. However, high temperature causes detrimental effects on nutritional quality of juices such as reported in cashew apple and pineapple juice (Rawson et al., 2011). Consumers' demand for a preservation technology that retains fresh-like quality and, at the same time, ensures food safety has resulted in growing interest for non–thermal-processing methods. Both sonication and short-wave ultraviolet-C (UV-C) light treatment are alternative novel technologies to achieve the U.S. Food and Drug Administration (FDA) condition of a 5 log reduction of food borne pathogens in fruit juices (FDA, 2000; Salleh-Mack and Roberts, 2007).

Propagation of high-power ultrasound at low frequencies (20–100 kHz) in liquid causes cavitation (formation and collapse of bubbles). Consequently, these ‘tiny hotspots’ provide energy to disrupt microbial cell membrane and alter the properties of food (O'Donnell et al., 2010). The UV-C light (peak emission at 254 nm) exhibits germicidal effect by preventing the reproduction of microorganisms and eventually may result in cell death (Guerrero-Beltrán and Barbosa-Cánovas, 2004). Sonication and UV-C treatment are simple, reliable and cost-effective with improved efficiency (O'Donnell et al., 2010; Pala and Toklucu, 2013). These technologies have different mode of microbial inactivation, therefore being potential choices for a hurdle concept. The hurdle technology is a combination of preservation techniques that may have a synergistic effect on microbial destruction, with minimal impact on the quality of the food product (Leistner, 2000).

The purpose of this study was to compare the effects of combined treatment (sonication and UV-C) and thermal treatment on the quality parameters of Chokanan mango juice such as microbial inactivation, physicochemical properties (pH, total soluble solids (TSS) and titratable acidity), colour, clarity, browning index, hydroxymethyl furfural content, carotenoid content, ascorbic acid content and antioxidant activities. The information obtained from this study could serve to improve the progress of utilising combined treatment of ultrasonic and UV-C for preserving the quality of Chokanan mango juice.

Materials and methods

Chemicals

Gallic acid, L-ascorbic acid, ( + )-catechin, 5-hydroxymethyl furfural, 2,6-dichlorophenol-indophenol (DCPIP) sodium salt, potassium ferricyanide, ferric chloride, Folin-Ciocalteu reagent, sodium hydroxide, trichloroacetic acid, thiobarbituric acid and 2,2-diphenyl-1-picrylhydrazyl (DPPH) were purchased from Sigma (MO, USA). Metaphosphoric acid, aluminium chloride and peptone water were purchased from R&M Chemicals (Essex, UK). Sodium bicarbonate, sodium nitrite and sodium carbonate were purchased from BDH (Poole, UK). All chemical solvents used were analytical reagent grade and purchased from Sigma (MO, USA).

Extraction of mango juice

Ripe Chokanan mango fruits of uniform size and free from external defects were purchased from a local market (Selangor, Malaysia) located about 30 km from the Postharvest Biotechnology Laboratory, University of Malaya. The fruits were rinsed with running water and air-dried at room temperature (25 ℃ ± 1 ℃). Each mango was peeled, and the seed was discarded. Mango pulp was macerated using a domestic juice extractor (Philips Juice Extractor HR 2820, Holland) and then centrifuged (Beckman J2-MI Centrifuge, California) at 12,000 rpm for 10 min at 4 ℃. The supernatant was filtered using a steel sieve with an approximate diameter of 2 mm to obtain the juice and remove any remaining fibre. The filtered juice samples were stored in sterile glass bottles prior to deployment into experiment.

Experimental treatments

The freshly squeezed mango juice was treated by four paired combinations of selected non-thermal technologies. Sonication was employed as the first hurdle followed by UV-C treatment. Selection of processing variables was based on preliminary studies on stand-alone treatments to achieve significant microbial reduction and quality retention (Santhirasegaram et al., 2013, unpublished data).

The following terms were used to describe different treatments in this study:

Control (freshly squeezed or no treatment);

TT (thermal treatment);

S15 + U15 (combined sonication for 15 min and UV-C treatment for 15 min);

S30 + U15 (combined sonication for 30 min and UV-C treatment for 15 min);

S15 + U30 (combined sonication for 15 min and UV-C treatment for 30 min);

S30 + U30 (combined sonication for 30 min and UV-C treatment for 30 min).

All treatments and analysis were carried out in triplicates.

Thermal treatment

Mango juice (50 mL) stored in glass bottles was pasteurised in a covered water bath (Memmert, Germany) at 90 ℃ ± 1 ℃ for 60 s. After thermal treatment, the juice samples were immediately cooled to room temperature (25 ℃ ± 1 ℃) by immersing in an ice-water bath.

Sonication

The sonication of mango juice (50 mL) was performed using an ultrasonic cleaning bath (Branson Model 3510 Ultrasonic Cleaner, CT, USA) at 40 kHz frequency, as described by Santhirasegaram et al. (2013). The processing time was 15 and 30 min under dark condition. The actual power dissipated in the ultrasonic bath was 68–72 W, and the acoustic energy density was 1.36–1.44 W/cm³, which was determined by calorimetric method (Sutkar and Gogate, 2009; Gogate et al., 2011).

UV-C treatment

Juice samples were exposed to UV-C light under batch conditions. Mango juice (50 mL) was poured into four sterile Petri dishes (11 cm diameter, 0.8-cm fluid depth) and then exposed to a germicidal fluorescent UV-C lamp (30 W, 89.3 cm length, 25.5 cm diameter, Sankyo Denki, Japan) in a laminar flow cabinet (Gelman Science Biological Safety Cabinet Class II, NSW, Australia). The UV-C lamp has a peak emission at 254 nm. The distance between the juice surface and the UV-C lamp was 35 cm. The UV-C lamps were allowed to stabilise for 30 min prior to use. The duration of exposure was 15 and 30 min at 25 ℃ ± 1 ℃. The mean of UV radiation dose received by each juice sample is 3.525 J/m² (Keyser et al., 2008). Juice samples were bottled directly after treatment.

Physicochemical analysis (pH, TSS and titratable acidity)

Mango juice pH was determined using a pH metre (Hanna Microprocessor pH 211, Italy) at 25 ℃ ± 1 ℃. TSSs were determined using a digital refractometre (Atago PR-1 digital refractometre, Tokyo, Japan) at 25 ℃ ± 1 ℃, and results were expressed in standard °Brix unit.

For determination of titratable acidity, diluted mango juice was titrated with standardised 0.1 N sodium hydroxide to a definite faint pink end point using phenolphthalein as an indicator. The titratable acidity (%TA) was calculated (Sadler and Murphy, 2010) using the following equation

% TA = (V_{1} \times 0.1 NNaOH \times Eq . wt . \times 100) / (V_{2} \times 1000)

where V₁ is volume of titrant (mL), Eq. wt. is equivalent weight of anhydrous citric acid (64 mg/mEq) and V₂ is volume of sample (mL).

Colour, clarity, non-enzymatic browning index and 5-hydroxymethyl furfural content

The colour of juice samples was measured using a Chroma Meter (Minolta Chroma Meter CR-200, Minolta, Osaka, Japan). The colour parameters L* (lightness), a* (redness/greenness) and b* (yellowness/blueness) were evaluated. Colour differences (ΔE), in comparison to control (Caminiti et al., 2011), were calculated using the following equation

Δ E = [(Δ L *) 2 + (Δ a *) 2 + (Δ b *) 2] 1 / 2

Transmittance at 660 nm was measured using a spectrophotometer (UV-200-RS Spectrophotometer, MRC, Israel) to determine clarity (Glevitzky et al., 2008) against a blank (distilled water). High percentage of transmittance at 660 nm corresponds to high clarity.

Non-enzymatic browning index (NEBI) and 5-hydroxymethyl furfural (HMF) assay were carried out according to the method by Cohen et al. (1998). A standard curve of HMF (y = 0.0406x, r² = 0.9967) was prepared, and results were expressed as milligrams of HMF per litre juice sample.

Total carotenoid content

Carotenoid was extracted according to Lee et al. (2001), while the total carotenoid content (Scott, 2001) using β-carotene as a reference was calculated using the following formula:

Totalcarotenoidcontent = (A \times V_{1} \times C 1 %) / A 1 %

where A is absorbance reading of the diluted sample, V₁ is dilution factor, A^1% is absorbance of a 1% solution (the extinction coefficient for β-carotene; 2592 AU) and C^1% is concentration of a 1% solution (10 mg/mL).

Ascorbic acid content

Ascorbic acid content in samples was determined based on the DCPIP visual titration method (Ranganna, 1977). Results obtained were expressed as milligrams of ascorbic acid per 100 mL sample.

Antioxidant activity (total polyphenol and flavonoid content, DPPH radical scavenging and reducing power assay)

Antioxidants were extracted according to Santhirasegaram et al. (2013) using 80% methanol.

Total polyphenol content of juice samples was determined using Folin-Ciocalteu assay (Singleton et al., 1965) modified to a microscale (Bae and Suh, 2007). A standard curve of gallic acid (y = 0.00566x, r² = 0.9955) was prepared, and results were reported as milligrams of gallic acid equivalent (GAE) per 100 mL juice extract.

Total flavonoid content of juice samples was determined using a colorimetric method described by Sakanaka et al. (2005). A standard curve of ( + )-catechin (y = 0.0135x, r² = 0.9943) was prepared, and results were reported as milligrams of catechin equivalent (CE) per 100 mL juice extract.

DPPH radical scavenging assay was carried out as described by Oyaizu (1986) and Bae and Suh (2007). A standard curve of ascorbic acid (y = 10.145x, r² = 0.9907) was prepared, and results were reported as micrograms of ascorbic acid equivalent (AAE) per millilitre juice extract. The radical scavenging activity was calculated accordingly

% DPPHinhibition = (A_{control} - A_{sample} / A_{control}) \times 100

where A_control is absorbance reading of control and A_sample is absorbance reading of the sample.

A spectrophotometric method by Oyaizu (1986) was used for measuring the reducing power of juice samples. A standard curve of ascorbic acid (y = 0.0014x, r² = 0.9906) was prepared, and results were reported as micrograms of AAE per milliliter juice extract.

Microbial inactivation analysis

The 3M Petrifilm plate methods are recognised as AOAC International Official Methods of Analysis (3M Food Safety, 2010). Microbial count of juice samples was determined using Petrifilm plates (3M Center, MN, USA) for aerobic bacteria, coliform, yeast and mould according to Santhirasegaram et al. (2013). Results were expressed as log (CFU/mL).

Statistical analysis

Data obtained were subjected to statistical analysis using SPSS 19.0 software (SPSS Inc., IBM). In this study, data were represented as mean values ± standard deviation. The significant differences between mean values of juice samples were determined by analysis of variance (one way-ANOVA) using Tukey's HSD (honestly significant difference) test at a significance level of p < 0.05.

Results and discussion

Physicochemical analysis (pH, TSS and TA)

The pH, TSS and TA of juice (Table 1) showed no significant changes after thermal and combined treatment. Values for pH (4.58 to 4.63), TSS (14.5 to 14.7 °Brix) and TA (0.19 to 0.22%) of treated juice samples still lie within the range of standards desirable for freshly squeezed Chokanan mango juice. These observations are in agreement with a previous study reporting non-significant deviations of physicochemical parameters of juice processed by either thermal, ultrasound or UV-C, such as in apple and cranberry juice blend as well as orange and carrot juice blend (Caminiti et al., 2011, 2012).

Table 1.

Effects of thermal and combined treatment on physicochemical analysis (pH, total soluble solids, titratable acidity) of Chokanan mango juice.^a,b

Treatment	pH	Total soluble solids (°Brix)	Titratable acidity (%)
Control	4.62 ± 0.02 a	14.7 ± 0.06 a	0.20 ± 0.02 a
TT	4.58 ± 0.02 a	14.6 ± 0.05 a	0.19 ± 0.01 a
S15 + U15	4.59 ± 0.01 a	14.6 ± 0.08 a	0.22 ± 0.01 a
S30 + U15	4.60 ± 0.01 a	14.7 ± 0.06 a	0.21 ± 0.02 a
S15 + U30	4.61 ± 0.02 a	14.5 ± 0.05 a	0.21 ± 0.01 a
S30 + U30	4.63 ± 0.01 a	14.5 ± 0.08 a	0.19 ± 0.02 a

Values followed by different letters within the same column are significantly different (p < 0.05) (n = 9).

Control (freshly squeezed or no treatment); TT (thermal treatment); S15 + U15 (combined sonication for 15 min and UV-C treatment for 15 min); S30 + U15 (combined sonication for 30 min and UV-C treatment for 15 min); S15 + U30 (combined sonication for 15 min and UV-C treatment for 30 min); S30 + U30 (combined sonication for 30 min and UV-C treatment for 30 min).

Colour, clarity, NEBI and HMF content

Significant differences in colour of juice samples were observed between control and treatments (combined method and thermal), as shown in Table 2. An increase in lightness (L^*) and decrease in redness ( + a*) and yellowness ( + b*) were observed after all treatments. The increase in L* values could be attributed to the brightening effect of juice due to cavitational collapse of bubbles during sonication and UV-C photodegradation of coloured compounds (Bhat et al., 2011; Tiwari et al., 2008). The b* value is an indicator of the level of natural pigments (mostly carotenoids) responsible for the yellow colour of mango juice. Thus, the decrease in + b* value may be due to isomerisation of carotenoids, as previously reported by Rattanathanalerk et al. (2005) in thermal-treated pineapple juice. According to Cserhalmi et al. (2006), differences in colour parameters (ΔE) can be categorised as not noticeable (0 < ΔE < 0.5), slightly noticeable (0.5 < ΔE < 1.5), noticeable (1.5 < ΔE < 3.0), well visible (3.0 < ΔE < 6.0) and greatly visible (6.0 < ΔE < 12). In comparison to thermal treatment, combined treated samples S15 + U15, S30 + U15 and S15 + U30 showed lowest variation from the control, therefore falling within the ‘slightly noticeable’ range. However, an increase in ΔE corresponding to increased ultrasonic treatment time was observed, regardless of the UV-C treatment. Thus, sonication could be responsible for the colour degradation observed in this hurdle system, as previously suggested by Cheng et al. (2007) in guava juice treatment.

Table 2.

Effects of thermal and combined treatment on colour of Chokanan mango juice.^a,b

Treatment	Colour parameters
Treatment	L *	a *	b *	ΔE
Control	70.28 ± 0.05 a	5.00 ± 0.03 a	54.45 ± 0.04 a	–
TT	72.26 ± 0.11b	3.27 ± 0.11b	51.23 ± 0.15 b	4.16 ± 0.08 a
S15 + U15	70.55 ± 0.15 ac	4.72 ± 0.05 c	53.85 ± 0.03 c	0.72 ± 0.02 b
S30 + U15	70.78 ± 0.05 c	4.89 ± 0.02 ac	53.55 ± 0.08 c	1.04 ± 0.06 c
S15 + U30	70.76 ± 0.12 c	4.64 ± 0.13 c	53.88 ± 0.05 c	0.83 ± 0.12 b c
S30 + U30	71.68 ± 0.07 d	4.46 ± 0.09 d	52.94 ± 0.10 d	2.17 ± 0.10 d

Values followed by different letters within the same column are significantly different (p < 0.05) (n = 9).

Clarity acts as an indicator of the degree of turbidity of fruit juices. The clarity of juice (Table 3) showed significant decrease after thermal treatment. Thermal-treated samples showed the least clarity (7.30), when compared to the control (25.50), thus indicating the highest percentage of turbidity. This could be explained by the properties of heat, wherein particle sizes become larger, resulting in protein coagulation and negatively altering the rheology of juice samples (Aguiló-Aguayo et al., 2009). In contrast, significant improvement in clarity was observed in all combined treated samples. The highest increase in clarity (12%) was exhibited by S30 + U15 sample. In addition, there is an increasing trend in clarity corresponding to sonication time. This observation is mainly due to implosion shock waves during cavitation that breakdown macromolecules and colloidal particles, thus reducing the viscosity of juice and improving the clarity (Abid et al., 2013).

Table 3.

Effects of thermal and combined treatment on clarity, non-enzymatic browning index, HMF, total carotenoid and ascorbic acid content of Chokanan mango juice.^a,b,c

Treatment	Clarity (transmittance at 660 nm)	NEBI (absorbance at 420 nm)	HMF (mg/L)	Total carotenoid content (µg/100 mL)	Ascorbic acid content (mg/100 mL)
Control	25.50 ± 0.22 a	0.06 ± 0.00 a	0.60 ± 0.03 a	82.03 ± 1.29 a	8.91 ± 0.51 a
TT	7.30 ± 0.14 b	0.13 ± 0.01 b	1.12 ± 0.05 b	48.92 ± 1.32 b	3.10 ± 0.62 b
S15 + U15	27.40 ± 0.22 c	0.07 ± 0.00 a	0.67 ± 0.02 a	90.60 ± 1.52 c d	7.92 ± 0.38 c
S30 + U15	28.55 ± 0.14 d	0.07 ± 0.01 a	0.71 ± 0.05 a	93.65 ± 2.10 d	7.72 ± 0.11 c
S15 + U30	26.02 ± 0.35 e	0.07 ± 0.01 a	0.69 ± 0.02 a	88.29 ± 1.43 c	7.88 ± 0.29 c
S30 + U30	27.64 ± 0.12 c	0.11 ± 0.00 c	0.98 ± 0.07 b	94.70 ± 1.80 d	6.33 ± 0.55 d

Values followed by different letters within the same column are significantly different (p < 0.05) (n = 9).

HMF: 5-hydroxymethyl furfural; NEBI: non-enzymatic browning index.

The NEBI indicates browning of juice due to Maillard process (Caminiti et al., 2011), while HMF is one of the intermediates produced during this reaction (Rattanathanalerk et al., 2005). A significant increase in NEBI of juice (Table 3) subjected to thermal treatment was observed. Accordingly, HMF content also increased in thermal-treated samples (1.12 mg/L) when compared to the control (0.60 mg/L). This is a clear indication that heat accelerated the formation of browning compounds, consequently darkening the juice thus contributing to the highest increase in NEBI value and HMF. Likewise, enhanced browning index and HMF formation were observed in heat-treated strawberry juice (Aguiló-Aguayo et al., 2009). The results of NEBI and HMF agree with colour analysis for thermal-treated samples, whereby the decrease in + b* and increase in L* values denoted the colour change from yellow towards light brown. Conversely, combined treated samples, S15 + U15, S30 + U15 and S15 + U30, except S30 + U30, showed no significant variation in NEBI and HMF content, when compared to the control. This is consistent with the study conducted by Caminiti et al. (2011) on apple and cranberry juice blend subjected to combined non–thermal-processing methods, where no significant browning was promoted. Nevertheless, it is important to highlight that the concentration of HMF in all treated juice samples (thermal and combined method) were minimal and remained below the permitted limit (≤ 5 mg/L) by the Association of the Industry of Juices and Nectars from Fruits and Vegetables (AIJN, 1996).

Total carotenoid content

Juice samples subjected to thermal treatment exhibited significant loss of carotenoids (48.92 µg/100 mL) when compared to the control (82.03 µg/100 mL), as shown in Table 3. This could be attributed to the high temperature-induced degradation of main carotenoid pigments resulting in the rearrangement of structures (trans- to cis-form) and formation of epoxides (Rodríguez-Amaya, 1997). After combined treatment, juice samples showed significant enhancement (8 to 15%) in carotenoid content. S30 + U30 sample showed the highest increase in extractability of carotenoids (15%) when compared to the control. The modification of carotenoid-binding protein may improve the extraction yield of free carotenoids (Oms-Oliu et al., 2012). These phenomena were due to the sonochemical and UV photochemical reaction as a result of ultrasonic and UV-C treatment, respectively (Demirdoven and Baysal, 2008; Oms-Oliu et al., 2012). Therefore, the increased availability of free carotenoids possessing health promoting properties in combined treated juice samples is beneficial to consumers.

Ascorbic acid content

Ascorbic acid or commonly known as vitamin C possesses antioxidant properties that have been associated with protection against cancer (Block, 1991). There was significant reduction in ascorbic acid content in juice processed by thermal and combined method when compared to control (Table 3). For thermal-treated juice, a maximum reduction (65%) of ascorbic acid was exhibited when compared to the control. Similarly, significant loss of ascorbic acid was observed in thermal-processed orange juice, owing to its thermolabile characteristic (Pala and Toklucu, 2013). The least degradation of ascorbic acid after combined treatment was about 11% in S15 + U15 sample. The depletion of ascorbic acid occurs mainly due to oxidation induced by enzyme activities such as ascorbate oxidase and peroxidase (Oms-Oliu et al., 2012). Formation of hydroxyl radicals during UV photon generation and also by bubble implosion during sonication could be responsible for the decreased content of ascorbic acid (Bhat et al., 2011; Hart and Henglein, 1985). Minimal degradation of ascorbic acid content was observed in ultrasonic or UV-C-treated juices when compared to thermal treatment (Goh et al., 2012; Oms-Oliu et al., 2012). Hence, it is important to emphasise that combined treatment provides better retention of ascorbic acid when compared to thermal treatment due to the absence of heat supply.

Antioxidant activity (total polyphenol and flavonoid content, DPPH radical scavenging and reducing power assay)

The effects of treatments (thermal and combined method) on antioxidant activity in juice extracts are shown in Table 4. After thermal treatment, a significant reduction in total polyphenols and total flavonoids was observed. In contrast, a significant increase in extraction of polyphenols (23 to 37%) and flavonoids (29 to 35%) was exhibited in all combined treated juice samples when compared to control. The highest increase (37%) was from 97.83 mg GAE/100 mL to 134.01 mg GAE/100 mL in S30 + U15 sample for phenolic compounds. With regards to total flavonoids, the highest increase was for S30 + U30 sample (11.79 mg CE/100 mL), when compared to control (8.74 mg CE/100 mL). These observations are in agreement with a study by Abid et al. (2013), reporting significant increase in extractability of phenolic compounds and flavonoids in sonicated apple juice. The free radical generated by cavitation reacts with the aromatic ring of polyphenolics, thus contributing to their improvement in juice (Ashokkumar et al., 2008). Besides that, UV-C and ultrasound inactivate polyphenol oxidase enzyme, therefore preventing further loss of phenolic compounds (Bhat et al., 2011; Oms-Oliu et al., 2012). This is consistent with the study conducted by Bhat et al. (2011), where higher concentration of polyphenols and flavonoids was observed in starfruit juice after exposure to UV-C.

Table 4.

Effects of thermal and combined treatment on antioxidant activity of Chokanan mango juice.^a,b,c

Treatment	Total polyphenol content (mg GAE/100 mL)	Total flavonoid content (mg CE/100 mL)	DPPH radical scavenging activity (µg AAE/mL)	Reducing power (µg AAE/mL)
Control	97.83 ± 1.76 a	8.74 ± 0.12 a	8.29 ± 0.18 a	360.71 ± 3.20 a
TT	60.87 ± 1.42 b	6.52 ± 0.15 b	8.09 ± 0.15 a	345.10 ± 6.10 a
S15 + U15	120.46 ± 1.08 c	11.24 ± 0.19 c	8.55 ± 0.13 b	442.14 ± 4.12 b
S30 + U15	134.01 ± 1.53d	11.51 ± 0.07 c	9.01 ± 0.22 c	454.29 ± 2.87 c
S15 + U30	129.32 ± 1.38e	11.76 ± 0.23 c	8.63 ± 0.11 b	450.43 ± 5.15 c
S30 + U30	127.95 ± 1.87e	11.79± 0.25 c	8.24 ± 0.20 a	458.66 ± 6.11 c

Values followed by different letters within the same column are significantly different (p < 0.05) (n = 9).

AAE: ascorbic acid equivalent; CE: catechin equivalent; GAE: gallic acid equivalent.

Antioxidant activity may be evaluated by the ability to donate hydrogen to the stable-free radical DPPH or the reductive capacity by Fe^3 + to Fe^2 + transformation (Prabha and Vasantha, 2011). No significant changes were observed in percentage of DPPH inhibition after thermal treatment. Although thermal-treated juice samples showed a decrease in reducing power (345.10 µg AAE/mL), it was non-significant when compared to the control (360.71 µg AAE/mL). Similarly, Caminiti et al. (2012) reported that heat treatment did not induce significant changes in antioxidant capacity of orange and carrot juice blend. However, combined treated samples (S15 + U15, S30 + U15 and S15 + U30) exhibited significant increase in the percentage of DPPH inhibition compared to control. The highest percentage inhibition of DPPH was 91.4% (9.01 µg AAE/mL) for S30 + U15 sample, compared to the control, 84.1% (8.29 µg AAE/mL). Accordingly, all combined treated samples showed increase in reducing capacity. The maximum increase (27%) was from 360.71 µg AAE/mL to 458.66 µg AAE/mL in S30 + U30 sample. Previous studies have reported that non–thermal-processing methods increase extractability of antioxidants, such as observed in sonicated apple juice and UV-C-treated starfruit juice (Abid et al., 2013; Bhat et al., 2011). Therefore, combined treated samples with enhanced antioxidant capacity will be an added advantage to health conscious consumers, as it plays a role in prevention of the degenerative processes (Block et al., 1992).

Microbial inactivation analysis (coliform count, aerobic plate count, total yeast and mould count)

Aerobic bacteria, coliform, yeast and mould counts in freshly squeezed Chokanan mango juice were 2.74 log CFU/mL, 1.00 log CFU/mL and 2.42 log CFU/mL, respectively. After thermal treatment and combined treatment, juice samples showed significant reduction of microbial count (p < 0.05), as shown in Table 5. Thermal treatment completely inactivated aerobic bacteria, coliform, yeast and mould in juice samples. This is consistent with the study conducted by Noci et al. (2008) on heat-treated apple juice, where microbial count was reduced to below detection limit (< 1 log CFU/mL). High temperature causes adverse effects on microbes by denaturing essential proteins and altering cell membrane, eventually inactivating microbial growth. Combined treatment reduced coliform count to below detection limits. For aerobic plate count, S30 + U30 sample exhibited 100% reduction of microbial count when compared to other combined treated samples, S15 + U15 (46%), S30 + U15 and S15 + U30 (64%). This could be explained by the properties of cavitation bubbles that induce microstreaming and shear stresses with high-localised pressure and temperature, resulting in the disintegration of the microbial cells (Abid et al., 2013). Additionally, absorption of UV light ray causes formation of cross-links between adjoining pyrimidine bases on the same DNA strand, thus exhibiting bactericidal effects (Pala and Toklucu, 2013; Walkling-Ribeiro et al., 2008).

Table 5.

Effects of thermal and combined treatment on microbial inactivation analysis of Chokanan mango juice.^a,b,c

Treatment	Coliform count (log CFU/mL)	Aerobic plate count (log CFU/mL)	Yeast and mould count (log CFU/mL)
Control	1.00 ± 0.02a	2.74 ± 0.01a	2.42 ± 0.02a
TT	NDb	NDb	NDb
S15 + U15	NDb	1.48 ± 0.02c	1.84 ± 0.05c
S30 + U15	NDb	1.00 ± 0.08d	1.50 ± 0.03d
S15 + U30	NDb	1.00 ± 0.02d	1.39 ± 0.03e
S30 + U30	NDb	NDb	1.00 ± 0.05f

Values followed by different letters within the same column are significantly different (p < 0.05) (n = 6).

CFU, colony-forming unit; ND, not detected.

As a hurdle, ultrasound and UV-C improve the rate of sterilisation of juice samples, which may be due to their synergistic effects. Previous studies have reported promising preservation of fruit juices by combined non–thermal-processing methods (Noci et al., 2008; Walkling-Ribeiro et al., 2008). In this study, the percentage of inactivation of total yeast and mould (24 and 59%) was lower than aerobic bacteria (46 to 100%) for combined treated samples, exhibiting maximum inactivation for S30 + U30 sample (59%). It was clearly exhibited that yeast and mould display greater resistance to sonication and UV-C due to difference in size of microbial cells and thickness of cell wall (Pala and Toklucu, 2013). However, complete inactivation of yeast and mould in juice samples was not observed in this study for all combined treated samples. Therefore, this hurdle sequence (ultrasound and UV-C) could be combined with mild heat or pressure treatment to enhance the decontamination efficiency.

Conclusions

Chokanan mango juice subjected to combined sonication and UV-C treatment (S15 + U15, S30 + U15 and S15 + U30) exhibited significant improvements in clarity, antioxidant capacity and extractability of carotenoids, phenolic compounds and flavonoids, when compared to freshly squeezed juice. In addition, combined treatment showed complete inactivation of coliforms and aerobic bacteria, along with significant reduction in yeast and mould count. Although thermal treatment was effective in completely inactivating microbial growth in juice, significant quality loss was observed. Combination of ultrasound and UV-C, therefore, is a promising hurdle for better retention of quality and a feasible alternative to thermal treatment. Further research work is needed to develop models to optimise the processing variables of this hurdle sequence, thus producing improved quality juice together with safety standards. Consequently, this study provides more attention for positive implementation of combined treatment on a pilot scale.

Footnotes

Funding

The authors thank the University of Malaya Postgraduate Research Fund [PV086/2012A] for supporting this research.

References

3M Food Safety. (2010). 3M Petrifilm interpretation guide. Available at: http://solutions.3m.com/wps/portal/3M/en_US/Microbiology/FoodSafety/ (accessed 2 July 2013).

Abid

Jabbar

Hashim

Lei

(2013) Effect of ultrasound on different quality parameters of apple juice. Ultrasonics Sonochemistry 20: 1182–1187.

Aguiló-Aguayo

Oms-Oliu

Soliva-Fortuny

Martín-Belloso

(2009) Changes in quality attributes throughout storage of strawberry juice processed by high-intensity pulsed electric fields or heat treatments. LWT-Food Science and Technology 42: 813–818.

Ashokkumar

Sunartio

Kentish

Mawson

Simons

Vilkhu

(2008) Modification of food ingredients by ultrasound to improve functionality: a preliminary study on a model system. Innovative Food Science & Emerging Technologies 9: 155–160.

Association of the Industry of Juices and Nectars from Fruits and Vegetables (AIJN) (1996) Association of the Industry of Juices and Nectars of the European Economic Community Code of Practice for Evaluation of Fruit and Vegetable Juices, Brussels: AIJN.

Bae

Suh

(2007) Antioxidant activities of five different mulberry cultivars in Korea. LWT-Food Science and Technology 40: 955–962.

Bhat

Ameran

Voon

Karim

Tze

(2011) Quality attributes of starfruit (Averrhoa carambola L.) juice treated with ultraviolet radiation. Food Chemistry 127: 641–644.

Block

(1991) Vitamin C and cancer prevention: the epidemiologic evidence. The American Journal of Clinical Nutrition 53: 270–282.

Block

Patterson

Subar

(1992) Fruit, vegetables, and cancer prevention: a review of the epidemiological evidence. Nutrition and Cancer 18: 1–29.

10.

Caminiti

Noci

Morgan

Cronin

Lyng

(2012) The effect of pulsed electric fields, ultraviolet light or high intensity light pulses in combination with manothermosonication on selected physico-chemical and sensory attributes of an orange and carrot juice blend. Food and Bioproducts Processing 90: 442–448.

11.

Caminiti

Noci

Munoz

Whyte

Morgan

Cronin

(2011) Impact of selected combinations of non-thermal processing technologies on the quality of an apple and cranberry juice blend. Food Chemistry 124: 1387–1392.

12.

Cheng

Soh

Liew

Teh

(2007) Effects of sonication and carbonation on guava juice quality. Food Chemistry 104: 1396–1401.

13.

Cohen

Birk

Mannheim

Saguy

(1998) A rapid method to monitor quality of apple juice during thermal processing. Lebensmittel-Wissenschaft & Technologie 31: 612–616.

14.

Cserhalmi

Sass-Kiss

Tóth-Markus

Lechner

(2006) Study of pulsed electric field treated citrus juices. Innovative Food Science & Emerging Technologies 7: 49–54.

15.

Demirdoven

Baysal

(2008) The use of ultrasound and combined technologies in food preservation. Food Reviews International 25: 1–11.

16.

Food and Agriculture Organisation of the United Nation Statistics Division, FAOSTAT (2013) Food and Agricultural commodities production. Available at: http://faostat.fao.org/site (accessed 26 July 2013).

17.

Food and Drug Administration (FDA) (2000) Irradiation in the production, processing and handling of food. Federal Register–Rules and Regulations 65: 71056–71058.

18.

Glevitzky

Pop

Brusturean

Bogdan

Calisevici

Perju

(2008) Efficient use of antioxidants to preserve fruit juice. Revista de Chimie (Bucureºti) 59: 1291–1295.

19.

Gogate

Sutkar

Pandit

(2011) Sonochemical reactors: Important design and scale up considerations with a special emphasis on heterogeneous systems. Chemical Engineering Journal 166: 1066–1082.

20.

Goh

Noranizan

Leong

Sew

Sobhi

(2012) Effect of thermal and ultraviolet treatments on the stability of antioxidant compounds in single strength pineapple juice throughout refrigerated storage. International Food Research Journal 19: 1131–1136.

21.

Guerrero-Beltrán

Barbosa-Cánovas

(2004) Advantages and limitations on processing foods by UV light. Food Science and Technology International 17: 137–147.

22.

Hart

Henglein

(1985) Free radical and free atom reactions in the sonolysis of aqueous iodide and formate solutions. The Journal of Physical Chemistry 89: 4342–4347.

23.

Keyser

Műller

Cilliers

Nel

Gouws

(2008) Ultraviolet radiation as a non-thermal treatment for the inactivation of microorganisms in fruit juice. Innovative Food Science & Emerging Technologies 9: 348–354.

24.

Lee

Castle

Coates

(2001) High-performance liquid chromatography for the characterization of carotenoids in the new sweet orange (Earlygold) grown in Florida, USA. Journal of Chromatography A 913: 371–377.

25.

Leistner

(2000) Basic aspects of food preservation by hurdle technology. International Journal of Food Microbiology 55: 181–186.

26.

Noci

Riener

Walkling-Ribeiro

Cronin

Morgan

Lyng

(2008) Ultraviolet irradiation and pulsed electric fields (PEF) in a hurdle strategy for the preservation of fresh apple juice. Journal of Food Engineering 85: 141–146.

27.

O'Donnell

Tiwari

Bourke

Cullen

(2010) Effect of ultrasonic processing on food enzymes of industrial importance. Trends in Food Science & Technology 21: 358–367.

28.

Oms-Oliu

Odriozola-Serrano

Martín-Belloso

(2012) The effects of non-thermal technologies on phytochemicals. In: Rao

(ed) Phytochemicals: A Global Perspective of Their Role in Nutrition and Health, Croatia: InTech, pp. 108–120.

29.

Oyaizu

(1986) Studies on products of browning reactions: antioxidative activities of products of browning reaction prepared from glucosamine. Japanese Journal of Nutrition 103: 413–419.

30.

Pala

Toklucu

(2013) Microbial, physicochemical and sensory properties 606 of UV-C processed orange juice and its microbial stability during refrigerated storage. 607. LWT-Food Science and Technology 50: 426–431.

31.

Prabha

Vasantha

(2011) Antioxidant, cytotoxicity and polyphenolic content of Calotropis procera (Ait.) R. Br. Flowers. Journal of Applied Pharmaceutical Science 1: 136–140.

32.

Ranganna

(1977) Chapter 5: ascorbic acid. In: Ranganna

(ed) Manual of Analysis of Fruit and Vegetable Products, New Dehli: Tata McGrawHill Publishing Company, pp. 94–96.

33.

Rattanathanalerk

Chiewchan

Srichumpoung

(2005) Effect of thermal processing on the quality loss of pineapple juice. Journal of Food Engineering 66: 259–265.

34.

Rawson

Patras

Tiwari

Noci

Koutchma

Brunton

(2011) Effect of thermal and non-thermal processing technologies on the bioactive content of exotic fruits and their products: review of recent advances. Food Research International 44: 1875–1887.

35.

Rivera

Cabornida

IMB

(2008) Development of ready-to-drink green mango juice. University of Southern Mindanao R&D Journal 16: 71–77.

36.

Rodríguez-Amaya

(1997) Carotenoids and Food Preparation: The Retention of Provitamin A Carotenoids in Prepared, Processed and Stored Foods, Washington, DC: OMNI.

37.

Sadler

Murphy

(2010) pH and titratable acidity. In: Nielsen

(ed) Food Analysis, New York: Springer, pp. 231–233.

38.

Sakanaka

Tachibana

Okada

(2005) Preparation and antioxidant properties of extracts of Japanese persimmon leaf tea (kakinoha-cha). Food Chemistry 89: 569–575.

39.

Salleh-Mack

Roberts

(2007) Ultrasound pasteurization: the effects of temperature, soluble solids, organic acids and pH on the inactivation of Escherichia coli ATCC 25922. Ultrasonics Sonochemistry 14: 323–329.

40.

Santhirasegaram

Razali

Somasundram

(2013) Effects of thermal treatment and sonication on quality attributes of Chokanan mango (Mangifera indica L.) juice. Ultrasonics Sonochemistry 20: 1276–1282.

41.

Scott

(2001) Detection and measurement of carotenoids by UV/VIS spectrophotometry. In: Wrolstad

Acree

Decker

Penner

Reid

Schwartz

(eds) Current Protocols in Food Analytical Chemistry, New York: John Wiley and Sons Inc, pp. F2.2.1–F2.2.10.

42.

Singleton

Joseph

Rossi

JRJA

(1965) Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents. American Journal of Enology and Viticulture 16: 144–158.

43.

Spreer

Ongprasert

Hegele

Wunsche

Muller

(2009) Yield and fruit development in mango (Mangifera indica L. cv. Chok Anan) under different irrigation regimes. Agricultural Waste Management 96: 574–584.

44.

Sutkar

Gogate

(2009) Design aspects of sonochemical reactors: techniques for understanding cavitational activity distribution and effect of operating parameters. Chemical Engineering Journal 55: 26–36.

45.

Tiwari

Muthukumarappan

O'Donnell

Cullen

(2008) Color degradation and quality parameters of sonicated orange juice using response surface methodology. LWT-Food Science and Technology 41: 1876–1883.

46.

Walkling-Ribeiro

Noci

Cronin

Riener

Lyng

Morgan

(2008) Reduction of Staphylococcus aureus and quality changes in apple juice processed by ultraviolet irradiation, pre-heating and pulsed electric fields. Journal of Food Engineering 89: 267–273.