A novel light source for post-harvest lettuce preservation based on chlorophyll absorption spectrum

Abstract

With increased consumers’ demand for safe and healthy food, LED lighting for photobiology has received wider attention. In order to prolong the preservation time of the post-harvest lettuce, this paper documents a novel light source designed for preservation based on the chlorophyll absorption spectrum. Effects of intermittent exposure (35 μmol m⁻² s⁻¹) on sensory quality and chlorophyll content in fresh lettuce were investigated during 3 days storage at 20°C ± 1°C and 60% ± 1% humidity using dark as the control. The results show that the lighting reduced the colour difference value of lettuce by 23.5% compared with the dark. The content of chlorophyll was 19.7% more than in the dark. The lighting with the novel light source inhibited the decline in the colour difference value −a/b of lettuce and delayed the degradation of chlorophyll.

1. Introduction

The use of pesticides has turned into a necessary component of farming systems throughout the world.¹ With the rapid development of agriculture, the use of pesticides, fertilisers and other chemical reagents has increased agricultural production, but it has caused serious harm to the ecosystem and threatened human health.^2–4 Consumers have become more interested in healthy, safe and green vegetables. LED lighting for photobiology, which is an integrated technology to improve agricultural production efficiency and promote human health through the energy transfer of light, has been gaining a lot of attention in the field of food.⁵ In plant growing, LED lighting for photobiology has been used in plant factories, which are highly automated, completely closed production systems in horticultural production, to improve the efficiency and quality of plant growth in a safe and green method, achieving high yields and quality production.⁶

Sunlight is the main source of energy for growing crops, but the light in the photosynthetically active radiation range, between approximately 400 nm and 700 nm, is not used uniformly, where only 4.6% to 6% of the total radiant energy from the sunlight is absorbed by plants for photosynthesis.^7,8 The morphology, physiology, photosynthetic efficiency and flowering capacity of plants are influenced by different light qualities.⁹

Plants contain many different plant pigments, such as chlorophylls, carotenoids and anthocyanins. The plant pigments play an important physiological and ecological role in plants. Crop yield is the result of the cumulative photosynthetic rate during the growing season. Photosynthetic pigments, such as chlorophylls and carotenoids, play pivotal roles in both light harvesting and photoprotection of the photosynthetic apparatus. Pigments such as anthocyanins, though not involved in light capture, act as photoprotectants, absorbing harmful UV rays, reducing photoinhibition and photodamage.^10–12

Plant factories had been using traditional agricultural lighting sources such as incandescent, high-pressure sodium and fluorescent lamps in the past.¹³ Although these light sources enable plants to be grown properly, the quality of light from these light sources is so mixed that most of the wavelengths in their spectrum have minimal effect on boosting crop growth.^14,15 At the same time, electrical energy consumption is extremely high for plant factories.¹⁶ Therefore, these light sources are not the most suitable electric light sources for plant factories. With the development of technology, LEDs are considered a prospective light source for agricultural lighting in the future. LEDs have a wide range of wavelength types that coincide with the spectrum of plant photosynthetic and photomorphogenic responses while having the advantages of adjustable spectrum, small size, low heat, high radiation and strong resistance to vibration.^17,18

In 1982, red LEDs were used for tomato supplementation in greenhouses in Japan.¹⁹ Since then, LEDs have been used as a light source for production in plant factories. Yanagi and Okamoto²⁰ discovered that the combination of red LEDs and blue LEDs resulted in a significant improvement in spinach morphological indicators compared to fluorescent lights. Wang et al.²¹ showed that the best growth of floral was with LEDs compared to incandescent lamps, fluorescent lamps and high-pressure sodium lamps. As study into plant growth continues, researchers have discovered that technology of light irritation is available for the preservation of fruit and vegetables.¹⁷ Broccoli irradiated with red LED for a period of 5 days had slower degradation of yellowing and chlorophyll compared with broccoli in darkness for an equivalent duration.²² Moreover, broccoli treated with red LED (660 nm) was more green than when illuminated with blue LED (470 nm) or white LED (430 nm to 730 nm).²³ Yellow LED and blue LED were shown to inhibit the growth of microorganisms in rocket leaves, whereas green LED and white LED alleviated chlorophyll degradation and increased carotenoids content in red chard.²⁴ White LED treatments at 10 μmol m⁻² s⁻¹ over a period of 7 days were able to maintain the chlorophyll and vitamin C content and maintain the appearance of bok choy compared with darkness.²⁵ At the same time, white LED showed the best preservation of lettuces that were irradiated for 21 days and had a greater content of chlorophyll and the total soluble solid after irradiation at 10 μmol m⁻² s⁻¹, compared with the red (630 nm), blue (450 nm) and green (526 nm) lighting.²⁶ Over an experimental period of 21 days, the tomatoes pretreated with blue LED (440 nm to 450 nm) had delayed softening.²⁷

Currently, the research in LED lighting for photobiology is focused on plant growth, poultry farming, aquaculture, health lighting and medical aesthetics, whereas the preservation of fruits and vegetables is still in the exploration stage. The demands of different vegetable species for light quality and light intensity are different, resulting in LEDs not being used appropriately.²⁸ Therefore, this study designed a novel light source to investigate its effect on post-harvest lettuce preservation quality, in order to provide a theoretical basis for improving the quality of post-harvest lettuce and prolonging the storage period.

2. Materials and methods

2.1 The novel light source

Post-harvest vegetables are still living individuals.²⁹ Under the appropriate light conditions, post-harvest vegetables are still able to accumulate photosynthetic material. Photosynthesis of plants absorbs about 60% of the light energy in the visible range, with the wavelengths 600 nm to 700 nm in the red–orange band and 400 nm to 500 nm in the blue band being the peak absorption regions. Plants accumulate photosynthetic material by absorbing light energy and converting it into chemical energy. The strongest absorption of the chlorophyll absorption spectrum is concentrated in the red light part of 640 nm to 660 nm and the blue light part of 430 nm to 450 nm. Chlorophyll a has two absorption peaks respectively at 430.6 nm and 660.9 nm. Chlorophyll b also has two obvious absorption peaks at 456.9 nm and 643.8 nm.³⁰ Therefore, the novel light source, where the spectrum corresponds to the plant absorption spectrum, probably has the ability to promote the photosynthesis of the lettuce after harvesting, which delays chlorophyll degradation, leaf yellowing and senescence.

Based on the visible light range, the spectrum of the novel light source for the post-harvest lettuce preservation was constructed with narrowband LEDs by means of the spectral superposition principle and the least squares method according to Equation (1):

Φ_{s} (λ) = \sum_{i = 1}^{n} k_{i} Φ_{i} (λ)

(1)

where Φ_s(λ) represents the spectrum power distribution, Φ_i(λ) represents the spectral power distribution of an LED (i = 1, 2, …, n) and k_i is the weight of LEDs for the matching spectral.

For a better comparison of the similarity between the fitted spectrum and target spectrum, the evaluation metric R² for the spectral fitting was calculated as shown in Equation (2):

R^{2} = 1 - \frac{\sum^{} {(y - - y_{e})}^{2}}{\sum^{} y^{2} - - {(\sum^{} y)}^{2} / n}

(2)

where y is the power distribution of the target spectrum, y_e is the power distribution of the fitted spectrum and n is the wavelength range. R² value is less than or equal to 1. When the value of R² is closer to 1, it means that the fitted spectrum and the target spectrum are more similar.³¹

Table 1 shows the number of LEDs required in the optical design, showing that a total of 17 narrowband LEDs were required for the best combination. The fitting evaluation index R² was 0.997.

Table 1

Parameters of narrowband LEDs

Numbers	Peak wavelength (nm)	FWHM	k_i	Amount
1	407	27	0.2137	2
2	420	15	0.1072	1
3	430	15	0.0967	1
4	446	24	0.6311	6
5	465	21	0.0631	1
6	471	28	0.0692	1
7	502	33	0.0244	1
8	532	33	0.0791	1
9	558	25	0.1077	1
10	588	17	0.0936	1
11	606	43	0.1846	2
12	621	17	0.0285	1
13	639	21	0.2219	2
14	643	17	0.2155	2
15	646	23	0.5337	5
16	661	24	0.1366	1
17	662	24	0.0885	1

There are limited varieties of narrowband LEDs in practical production. The LEDs in the simulation could not be bought in the exact same model, so the quantity was decreased. In order to match the design results as closely as possible, the narrowband LEDs selected contained the main wavelengths from the simulation results. Table 2 shows the parameters of the LEDs which were used for the experimental light source. There were 10 kinds of LEDs used for the novel light source, with a total of 24 pieces. The major LEDs with the highest numbers had peak wavelengths of approximately 440 nm to 450 nm and 640 nm to 650 nm, corresponding to the main wavelengths of the novel light source design results (Figure 1).

Table 2

Parameters and number of LEDs used

Numbers	Wavelength (nm)	Amount
1	420–430	2
2	440–450	6
3	460–465	1
4	470–475	1
5	500–510	1
6	520–530	1
7	570–575	1
8	590–595	1
9	620–630	1
10	640–650	9

Figure 1

Comparison of fitting spectrum and chlorophyll absorption spectrum

In Figure 2(a), the chromaticity coordinates of the experimental light source were (0.2695, 0.1029). Figure 2(b) shows the appearance of the novel light source. All the LEDs were placed in four concentric circles. The first concentric circle had a radius of 20 mm with the radius of each concentric circle differing by 20 mm. Six LEDs were arranged in the same circle with a circumference angle of 60°.

Figure 2

(a) The chromaticity diagram of the experimental light source; (b) image of the experimental light source

2.2 Plant material treatments and measurement

2.2.1 Plant material treatments

Lettuce (Lactuca sativa L.) was selected from freshly picked vegetables at the market. Samples were of similar size, without obvious pests and mechanical damage. Measurements were taken at random locations on the lettuce leaves with marking size 10 mm × 10 mm, at two locations each. Two treatment boxes (500 mm by 500 mm by 700 mm), each housed three lettuces. Two treatment boxes were placed in the same environment at a room temperature of 20°C ± 1°C and humidity of 60% ± 1%. Lighting group was treated with lighting for 12 h day⁻¹ for three days. The photosynthetical photon flux density (PPFD) of the light source was 35 μmol m⁻² s⁻¹ with a uniformity of 0.92, which was measured by the plant lighting analyser (PLA20, EVERFINE Corporation, Hangzhou, China). The measured surface size was 300 mm by 300 mm, with the distance from the light source at 700 mm.

2.2.2 Weight loss

Percent weight loss is an important indicator of change during the preservation of vegetables. Percent weight loss was calculated as shown in Equation (3):

Weight loss (%) = \frac{X_{0} - X}{X_{0}} \times 100

(3)

where X₀ is the initial weight and X is the weight after storage.²¹

2.2.3 Colour

Colour difference value provides a visual indication of the change in colour of vegetables during storage, with a larger −a/b indicating greener vegetables.³² The a* represents the red–green colour of the object. Meanwhile, b* indicates the yellow–blue colour of the object. The average of a* and b* was obtained for each marker point by repeating the measurement three times (CS-2000, Konica Minolta, Japan).

2.2.4 Chlorophyll

A portable chlorophyll meter (TYS-A, Zhongkeweihe, Beijing, China) was used to determine the relative chlorophyll content of the lettuces. The average of three measurements was repeated for each marker point.

The colour difference values, chlorophyll content and weight loss of the vegetables were measured at 12 h intervals.

2.3 Statistical analysis

The Kruskal–Wallis test was used for statistical analysis. All colour and chlorophyll measurements were normalised to the hour 0 level (before treatment) and expressed as the percentage of hour 0 level.³³ All figures were generated by Excel, MATLAB GraphPad Prism 8, Photoshop CC 2017 and Origin 2021.

3. Results and discussion

3.1 Effect of weight loss

As the duration of storage increases, there is a gradual increase in the loss of water from leafy greens. High rates of weight loss in green leafy vegetables lead to dehydration, resulting in reduced leaf turgor and increased susceptibility to physical damage. The sensory quality of green leafy vegetables is one of the most important factors for consumers to consider purchasing. In Figure 3, as the storage time increased, the weight loss rate of each experimental group showed a gradually increasing trend, which was always higher in the lighting group than in the dark group with the highest rate of weight loss between 12 h and 24 h. There was no significant difference (p > 0.05) in the weight loss rate of lettuce in the lighting group compared to the dark group during the whole storage period.

Figure 3

Effect on weight loss of lettuce. Values are means ± SEM (standard error of the mean) (n = 3)

The PPFD required for post-harvest preservation is low, which generally ranges from 10 μmol m⁻² s⁻¹ to 80 μmol m⁻² s⁻¹ used in various research reports.⁹ The PPFD used in this experiment was 35 μmol m⁻² s⁻¹ at a lower intensity. Twelve-hour intervals of exposure were used to avoid causing high weight loss rates in the light group. The results of this study are similar to Charles et al.,³⁴ in which weight loss up to 30% of the initial weight was observed in lettuce leaves stored for 7 days while exposed to continuous white light supplying 50 μmol m⁻² s⁻¹ to 150 μmol m⁻² s⁻¹. The results showed that LED light still favours accelerated water loss from vegetables with the effect increasing the longer the treatment time, even though they have the advantages of high radiation and low emissions of radiant heat.¹⁸ In addition to field conditions, light is also a regulator of stomatal opening during storage.³⁵ Lettuce under irradiation maintains a higher stomatal opening ratio, which accelerates the rate of weight loss.³⁶ However, light may also have the opposite effect of a modulatory mechanism that prevents dehydration by delaying fine senescence and reorganisation.³⁷

3.2 Effect of colour

Figure 4 shows the visual external aspect of lettuce in the light and dark treatment groups. After 60 h, the leaves of the lettuce in the dark group showed yellowing, and a little browning and slightly rotting. The colour difference visually reflects the colour change of vegetables in the storage process with a numerical value. The −a/b value was used to reflect the degree of green retention of lettuce due to the yellowing of lettuce during storage after harvesting. Figure 5 illustrates the trend of −a/b values of lettuce. In the lighting group, the −a/b values of lettuce showed an increasing and then decreasing trend with a peak value at the 12th hour. Lettuce under dark conditions −a/b values showed an overall decreasing trend indicating a gradual decrease in freshness during storage. There was a gradual shift from green to yellow. The −a/b value of the lighting group declined slowly throughout the storage period, which produced a significant difference (p < 0.05) from the rapidly declining dark group. Overall, the final values of −a/b for the lettuces treated with lighting were higher than for the dark group by 23.5%, which is similar to the results of the study by Kasim and Kasim.²⁶

Figure 4

Visual external aspect of lettuce in the lighting and dark

Figure 5

Effect on −a/b of lettuce. Values are means ± SEM (n = 3)

3.3 Effect of chlorophyll

The loss of chlorophyll is an indicator of the senescence of vegetables. As shown in Figure 6, the chlorophyll content of lettuce showed a decreasing trend. The degradation rate of chlorophyll content was lower in the lighting treatment group compared to the dark group. At the end of storage, the chlorophyll content of the light group was 19.7% higher than the dark control group. There were significant differences between the two groups throughout the preservation period (p < 0.05). From the results, the lighting group reduced the loss of chlorophyll to a certain extent after 60 h, indicating that lighting has an effect on slowing down the ageing of the post-harvest lettuce. These are in accordance with the results of Braidot et al.³⁸ who used white light treatment of lettuce to delay chlorophyll degradation.

Figure 6

Effect on chlorophyll of lettuce. Values are means ± SEM (n = 3)

Horticultural crops are severely stressed after harvest owing to a reduction in sources of energy, nutrients, hormones and water, which leads to the rapid initiation of senescence.³⁹ Initiation of senescence is highly dependent on light supply, among other things.⁴⁰ During storage, the quality of crops deteriorates due to the yellowing of leaves, which is also a result of chlorophyll degradation. Leaf yellowing results from the degradation of chlorophyll, which is a major post-harvest problem in lettuce. Previous studies have demonstrated that light irradiation inhibits chlorophyll degradation and also decreases chlorophyll-degrading enzyme activity and gene expression.^41,42 Kasim and Kasim²⁶ showed that all LED treatments significantly reduced yellowing in lettuce after 21 days at 5°C; white LED treatment significantly increased the chlorophyll content. Jin et al.⁴³ found that both fluorescent and LED green light treatments effectively delayed yellowing and senescence in broccoli florets. The results of the present experiment also showed that a dark environment accelerates chlorophyll degradation and senescence in post-harvest lettuce. Light is effective in delaying the degradation of chlorophyll in post-harvest lettuce.

4. Conclusions

Vegetables are usually placed in dark conditions during post-harvest storage, distribution and home refrigeration, which accelerates chlorophyll degradation and reduces vegetable quality such as colour, chlorophyll and Vc content. A novel light source was designed for the post-harvest lettuce preservation based on the chlorophyll absorption spectrum. Through the preservation experiments, differences in the effect of irradiation with this light source versus dark storage on lettuce quality were analysed. The results of the experiment showed that the novel light source irradiation increased the rate of weight loss in lettuce, but delayed yellowing and chlorophyll senescence, with colour difference values and chlorophyll degradation lower than the dark group by 23.5% and 19.7%.

Lighting for post-harvest preservation is safe, green and non-polluting, as well as simple and inexpensive to operate, satisfying consumer demand for safe, inexpensive and environmentally friendly food. Although the present study has some valuable results, there are still some limitations. The current experimental environment was only a simplified test that could not fully reflect the complex and variable environmental conditions in the real environment. In order to more accurately simulate the actual preservation process, the experimental environments that are closer to real conditions should be considered for future research. And more research on green leafy vegetables will be needed to provide more theoretical support for LED lighting preservation. The future research will better promote the development of the preservation technology of light radiation, which would provide a useful boost to the practical application in the field of vegetable preservation.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The work was financially supported by the General Project of Liaoning Provincial Education Department (JYTMS20230415).

ORCID iDs

Y-Y Zhu

G-Y Cao

References

Ataei

Gholamrezai

Movahedi

Aliabadi

An analysis of farmers’ intention to use green pesticides: the application of the extended theory of planned behavior and health belief model. Journal of Rural Studies 2020; 81: 374–384.

Hou

Wang

Inhibition or promotion? – the effect of agricultural insurance on agricultural green development. Front Public Health 2022; 10: 910534.

Grigoryeva

Dmitrevskaya

Belopukhov

Osipova

The chemical training of agrarian specialists: from the chemicalization of agriculture to green technologies. Sustainability 2022; 14: 8062.

Wang

Sarkar

Zhang

How capital endowment and ecological cognition affect environment-friendly technology adoption: a case of apple farmers of Shandong Province, China. International Journal Environmental Research Public Health 2021; 18: 7571.

Hitti

MacPherson

Orsat

Lefsrud

MG.

Comparison and perspective of conventional and LED lighting for photobiology and industry applications. Environmental and Experimental Botany 2020; 171: 103953.

Kozai

Resource use efficiency of closed plant production system with artificial light: concept, estimation and application to plant factory. Proceedings of the Japan Academy 2013; 89: 447–461.

Zhu

Long

Ort

DR.

What is the maximum efficiency with which photosynthesis can convert solar energy into biomass?

Current Opinion in Biotechnology 2008; 19: 153–159.

Long

Zhu

Naidu

Ort

DR.

Can improvement in photosynthesis increase crop yields?

Plant Cell Environ 2006; 29: 315–330.

D'Souza

Yuk

Khoo

Zhou

. Application of light-emitting diodes in food production, postharvest preservation, and microbiological food safety. Comprehensive Reviews in Food Science and Food Safety 2015; 14: 719–740.

10.

Simkin

Kapoor

Doss

CGP

Hofmann

Lawson

Ramamoorthy

The role of photosynthesis related pigments in light harvesting, photoprotection and enhancement of photosynthetic yield in planta. Photosynthesis Research 2022; 152: 23–42.

11.

Mirkovic

Ostroumov

Anna

Grondelle

Scholes

GD.

Light absorption and energy transfer in the antenna complexes of photosynthetic organisms. Chemical Reviews 2017; 117: 249–293

12.

Zhang

Bian

Yuan

Chen

CG.

A review on the effects of light-emitting diode (LED) light on the nutrients of sprouts and microgreens. Trends in Food Science and Technology 2020; 99: 203–216

13.

Kim

Hahn

Heo

Paek

KY.

Effects of LEDs on net photosynthetic rate, growth and leaf stomata of chrysanthemum plantlets in vitro. Scientia Horticulturae 2004; 101: 143–151.

14.

Chen

YM.

Development of agricultural light sources. China Light and Lighting 2015; 365: 5–10+15.

15.

Ahmed

Tong

Yang

QC.

Optimal control of environmental conditions affecting lettuce plant growth in a controlled environment with artificial lighting: a review. South African Journal of Botany 2020; 130: 75–89

16.

Gupta

Jatothu

Fundamentals and applications of light emitting diodes (LEDs) in in vitro plant growth and morphogenesis. Plant Biotechnology Reports 2013; 7: 211–220.

17.

Perera

WPTD

Navaratne

Wickramasinghe

. Impact of spectral composition of light from light-emitting diodes (LEDs) on postharvest quality of vegetables: a review. Postharvest Biology and Technology 2022; 191: 111955.

18.

Branas

Azcondo

Alonso

JM.

Solid-state lighting: a system review. IEEE Industrial Electronics Magazine 2013; 7: 6–14.

19.

Yang

QC.

Application and prospect of light-emitting diode (LED) in agriculture and bio-industry. Journal of Agricultural Science and Technology 2008; 10: 42–47.

20.

Yanagi

Okamoto

Utilization of super-bright light emitting diodes as an artificial light source for plant growth. International Symposium on Artificial Lighting in Horticulture, Noordwijkerhout, The Netherlands, 1997: 223–228.

21.

Wang

Zhuang

ML.

Lamp distribution design for adjustment of florescence in floral production. Agricultural Science and Technology 2013; 14: 1629–1631.

22.

Jiang

Zuo

Zheng

Guo

Gao

Zhao

, et al. Red LED irradiation maintains the postharvest quality of broccoli by elevating antioxidant enzyme activity and reducing the expression of senescence-related genes. Scientia Horticulturae 2019; 251: 73–79.

23.

Zhang

Setiawan

Yamawaki

Asai

Nishikawa

, et al. Effect of red and blue LED light irradiation on ascorbate content and expression of genes related to ascorbate metabolism in postharvest broccoli. Postharvest Biology and Technology 2014; 94: 97–103.

24.

Pennisi

Orsini

Castillejo

Gómez

Crepaldi

Fernández

, et al. Spectral composition from led lighting during storage affects nutraceuticals and safety attributes of fresh-cut red chard (Beta vulgaris) and rocket (Diplotaxis tenuifolia) leaves. Postharvest Biology and Technology 2021; 175: 111500.

25.

Zhou

Zuo

Gao

Wang

Jiang

Low intensity white light-emitting diodes (LED) application to delay senescence and maintain quality of postharvest pakchoi (Brassica campestris L. ssp. chinensis (L.) Makino var. communis Tsen et Lee). Scientia Horticulturae 2020; 262: 109060.

26.

Kasim

While continuous white LED lighting increases chlorophyll content (SPAD), green LED light reduces the infection rate of lettuce during storage and shelf-life conditions. Journal of Food Processing and Preservation 2017; 41: e13266.

27.

Dhakal

Baek

K-H.

Short period irradiation of single blue wavelength light extends the storage period of mature green tomatoes. Postharvest Biology and Technology 2014; 90: 73–77.

28.

Sipos

Boros

Csambalik

Székely

Jung

Balázs

Horticultural lighting system optimalization: a review. Scientia Horticulturae 2020; 273: 109631.

29.

Zhan

Zhang

CC.

Research progress on lighting emitting diode (LED) irradiation effect on fresh fruits and vegetables storage. Food and Fermentation Industries 2018; 44: 264–269, 278.

30.

Effect of light on synthesis of chlorophylls. Modern Agricultural Science and Technology 2014; 21: 161–164.

31.

Cao

Zhang

Yang

Sun

Wang

, et al. Solar spectrum matching with white OLED and monochromatic LEDs. Applied Optics 2018; 57: 2659.

32.

Nájera

Guil-Guerrero

Enríquez

Álvaro

Urrestarazu

LED-enhanced dietary and organoleptic qualities in postharvest tomato fruit. Postharvest Biology and Technology 2018; 145: 151–156.

33.

Song

Qiu

Gao

Kuai

Molecular and physiological analyses of the effects of red and blue LED light irradiation on postharvest senescence of pakchoi. Postharvest Biology and Technology 2020; 164: 111155.

34.

Charles

Nilprapruck

Roux

Sallanon

Visible light as a new tool to maintain fresh-cut lettuce post-harvest quality. Postharvest Biology and Technology 2018; 135: 51–56.

35.

Kinoshita

Doi

Suetsugu

Kagawa

Wada

Shimazaki

KI.

Phot1 and phot2 mediate blue light regulation of stomatal opening. Nature 2001; 414: 656.

36.

Martínez-Sánchez

Tudela

Luna

Allende

Gil

MI.

Low oxygen levels and light exposure affect quality of fresh-cut Romaine lettuce. Postharvest Biology and Technology 2011; 59: 34–42.

37.

Guo

Wang

ZQ.

Respiratory pathway metabolism and energy metabolism associated with senescence in postharvest Broccoli (Brassica oleracea L. var. italica) florets in response to O2/CO2 controlled atmospheres. Postharvest Biology and Technology 2016; 111: 330–336.

38.

Braidot

Petrussa

Peresson

Patui

Bertolini

Tubaro

, et al. Low-intensity light cycles improve the quality of lamb’s lettuce (Valerianella olitoria [L.] Pollich) during storage at low temperature. Postharvest Biology and Technology 2014; 90: 15–23.

39.

King

Morris

SC.

Early compositional changes during postharvest senescence of broccoli. Journal of the American Society for Horticultural Science 1994; 119: 1000–1005.

40.

Büchert

Gómez Lobato

Villarreal

Civello

Martínez

GA.

Effect of visible light treatments on postharvest senescence of broccoli (Brassica oleracea L.). Journal of the Science of Food and Agriculture 2010; 91: 355–361.

41.

Hasperué

Guardianelli

Rodoni

Chaves

Martínez

GA.

Continuous white–blue LED light exposition delays postharvest senescence of broccoli. LWT – Food Science and Technology 2016; 65, 495–502.

42.

Aiamla

Kaewsuksaeng

Shigyo

Yamauchi

Impact of UV-B irradiation on chlorophyll degradation and chlorophyll-degrading enzyme activities instored broccoli (Brassica oleracea L. Italica Group) florets. Food Chemistry 2010; 120: 645–651.

43.

Jin

Yao

Wang

Zheng

YH.

Effect of light on quality and bioactive compounds in postharvest broccoli florets. Food Chemistry 2015; 172: 705–709.