WO2018122860A1

WO2018122860A1 - System and method for early detection for prevention of postharvest chilling injury

Info

Publication number: WO2018122860A1
Application number: PCT/IL2018/050007
Authority: WO
Inventors: Alkin NOAM
Original assignee: US Department of Agriculture USDA; MINISTRY OF AGRICULTURE
Current assignee: US Department of Agriculture USDA; MINISTRY OF AGRICULTURE
Priority date: 2017-01-02
Filing date: 2018-01-02
Publication date: 2018-07-05
Anticipated expiration: 2019-07-02

Abstract

Aspects of the present invention include detection of volatile compounds related to response of vegetable or fruit, (e.g., mango), as result of stress like suboptimal temperature. Such response may lead to activation of some metabolic pathways that can induce synthesis of volatile compounds which may serve according to embodiments of the present invention as signals which indicate onset of CI and/or deterioration of fruit quality. The release of such volatiles compounds may be detected long before CI symptoms become notable. According to some embodiments of the invention, output from sensors detecting presence of volatile compounds indicating that fruits are starting to suffer from chilling stress, are received by at least one control module which operates conditioning system so as to alter storage conditions for avoiding CI and/or quality deterioration of fruits or vegetables.

Description

SYSTEM AND METHOD FOR EARLY DETECTION FOR PREVENTION OF POSTHARVEST CHILLING INJURY

TECHNICAL FIELD

The present invention relates to the field of postharvest treatment. More particularly, the invention relates to a system and methods for early detection for prevention of postharvest deterioration of quality of agricultural product in storage.

BACKGROUND

Postharvest cold storage is widely used to prolong the storage time of fresh produce.

Cold storage is considered the most effective method of prolonging storage of fresh produce, because it maintains fruit quality and defers fruit deterioration. Cold storage slows down cellular respiration rate and ripening-related metabolic processes in fruit. Thus, as the fruit is stored at a lower temperature the fruit storage period is extended and fruit deterioration is inhibited. Optimal cold storage conditions can reduce weight loss and fruit rot, however storage at suboptimal temperatures disrupts a number of metabolic processes.

As an example mango is consumed worldwide for its delicious taste and aroma and nutritional qualities. Mango fruit is stored at 10-12 °C; however storage at lower temperature causes chilling injury (CI), reduced fruit quality and even fruit loss. In mango, CI symptoms include lenticel discoloration and pitting on the peel, internal breakdown, uneven ripening, poor color development, and reduced aroma and flavor. Thus, the fruit with CIs ripens with reduced development of normal flavor and aroma.

According to current post-harvest practices, storage conditions are determined based mainly on a sort of cumulative experience and know-how. Reference to the real-time agricultural product quality changes if being made at all is done unsystematically, typically based on visual observation by a humans, or in some cases, usually when it is too late, based on chilling symptoms on the fruit. This involves in many cases a delayed and inaccurate response to metabolic processes in crop that may lead to irreversible spoilage. The terms "crop", "fruit", "vegetable" and "agricultural product" may be used interchangeably hereinafter. Basically, storage at lower temperature without chilling allow longer storage. However, storage at suboptimal lower temperatures for long periods leads to CI symptoms, decreased fruit flavor and quality and ultimately, fruit loss.

The following table illustrates some known storage temperatures acceptable for number of agricultural product s, although there are variations among various cultivars and different ripening stages.

Metabolisms in agricultural product may be affected by post-harvest conditions, such as temperature, irradiation, the surrounding gaseous composition, and the chemicals being used. Consideration has been given to a possible use of various additives in attempt to enhance resistance to decay. For example, some fruits showed longer shelf-life times with acceptable quality in response to addition of hexanal, probably as consequence of activation of natural defense response in the harvested fruit. Hexanal may act as signaling intra-plant and/or inter- plant. Thus, for example, when leaves are being damaged by herbivores or pathogens, they begin to produce hexanals, some of which may induce defense responses. However treating agricultural products by additives is not related, thus it has no effect on responding to realtime metabolic processes occurring in agricultural product during cold storage. BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments, features, aspects and advantages of the present invention are described herein in conjunction with the following drawings:

Figure 1. schematically illustrates upregulation of α-linolenic acid-oxidation pathway genes in response to suboptimal cold storage

Figure 2. Heat map of relative expression of genes in the α-linolenic acid-oxidation pathway at two different storage temperatures (5 °C and 12 °C) at different sampling times (2, 7 and 14 days) compared to harvest time.

Figure 3. shows table of transcripts relative expression values of α-linolenic acid-oxidation pathway and their abbreviations

Figure 4 (A-E). shows a table of volatile compounds concentrations in μg/g FW, found in mango fruit peels at harvest, and during cold storage at 12°C and suboptimal (5°C) temperatures

Figure 5. schematically illustrates changes in C₆ and C9 volatile concentrations during cold storage at 12°C and suboptimal (5°C) temperatures

SUMMARY OF EMBODIMENTS OF THE INVENTION

The present invention is intended to overcome the deficiencies of the background art by a real-time monitoring of agricultural product quality during storage relying on early detection of metabolisms occurring in the stored products in response to suboptimal temperatures which may lead to deterioration of quality of crops, e.g., mango, pomegranate, avocado, citrus, pepper, lattice, apple, pear, cherry, peach, grape, banana, and tomato. According to some aspects of the invention an early detection of onset of metabolism, associated with crop response to chilling and quality deterioration, is based on changes in production of volatile compounds by a product being exposed to stress conditions during storage. The presence of volatile compounds related with early phases of such metabolisms, could be detectable before the symptoms of such deterioration become notable. Deterioration in agricultural product quality may include appearance of Chilling Injury (CI). The evaluation and determination of agricultural product quality may include the extent of the appearance of CI symptoms which are frequently caused by sub-optimal storage temperature. A system for prevention of post-harvest CI according to some embodiments of the above aspects may include at least one sensor capable of detecting a presence or measuring concentrations of at least one volatile compound which is indicative of CI and/or product quality deterioration. Such volatile compounds may include at least one alkene, or at least one oxylipin e.g, 1- hexanal, (Zj-3-hexenal, (Zj-3-hexenol, (EJ-2-hexenal, nonanal, heptanal, octanal..

In some embodiments of the present invention, one computerized module capable of controlling an operation of a conditioning system is used. The terms "computerized module", "computerized control module", "control module", "module" and "controller" may be used interchangeably hereinafter. An operation of a conditioning system in a depot typically includes an adjustment of storage temperature. The terms "storage temperature", "temperature in a depot" and alike may be used interchangeably in this disclosure. Typically the control module processes input concerning presence and/or concentrations of at least one volatile compound which indicate agricultural product quality which may be associated with CI. The adjustment of the temperature in a depot may include elevation of this temperature whenever the above mentioned volatile compound is detected. Similarly, the adjustment of the temperature may be related to changes in concentrations of the above mentioned one or more volatile compounds. For example, when the concentration of such volatile compound increases, the conditioning system would receive a command from the control module to elevate the storage temperature. Lowering storage temperature can prolong storage time to as long as no CI occurs. According to some embodiments of the present invention the conditioning system may reduce depot temperature when there is no detection of the above mentioned volatile compound. According to an embodiment of the present invention altering of temperature may include reducing depot temperature whenever the presence of at least one volatile compound drops below a threshold level. Similarly reduction of storage temperature may be implemented when measurements indicate that the onset of rise of concentration of such a volatile compound decreases.

Some aspects of the present invention include methods for prevention of post-harvest chilling injury (CI). Such methods include detecting a presence or measuring concentrations of at least one volatile compound which is indicative for CI and/or agricultural product quality such as mango, pomegranate, avocado, citrus, pepper, apple, pear, cherry, peach, grape, banana, and tomato. The above methods may be particularly useful during cold storage in order to keep the storage temperature as low as possible while avoiding CI and/or quality deterioration. In some cases such methods may include also processing inputs concerning detection or measuring concentrations of the aforementioned volatile compound. Such processing of input may be utilized for altering conditions in a depot where agricultural product is being stored in order to respond and adjust conditions to avoid deterioration in agricultural product quality. Altering conditions in a depot may include according to some embodiments of the above aspects, elevation of storage temperature whenever detection of presence of the above mentioned volatile compound is occurred. Similarly the adjustment of the temperature may be according to changes in concentrations of the above mentioned volatile compound. For example, when a concentration of such volatile compound increases, the conditioning system would receive a command from the control module to elevate the storage temperature. According to some embodiments of the present invention the conditioning system may reduce depot temperature when there is no detection of the above mentioned volatile compound. Similarly reduction in storage temperature may be done when measurements are indicating that the concentration of such a volatile compound decreases. According to some embodiments of the above aspects a target value for storage temperature may be set according to certain requirements such as the type of crop in storage. In some examples embodying the above aspects, alteration of the storage temperature ranges between one Celsius degree below the target value to three degrees Celsius above the target value, (e.g., 10°C, 7°C, 5°C, 3°C, and 2°C).

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, aspects of the present invention are explained by way of example. However, it should be understood that the below examples are in no way limiting embodiments of the present invention which are applicable on other agricultural products. The present invention is intended to overcome the deficiencies of the background art by realtime monitoring of crop CI and/or quality during storage relying on early detection of metabolites that may lead to or indicate a CI and/or deterioration of quality of stored vegetable products, e.g., mango, pomegranate, avocado, citrus, pepper, lattice, apple, pear, cherry, peach, grape, banana, and tomato.

Aspects of the present invention include rely on response of vegetable or fruit to stress conditions such as suboptimal temperature. Such response may lead to activation of some metabolic pathways that can induce synthesis of volatile compounds which may serve according to embodiments of the present invention as signals which indicate beginning deterioration of fruit quality. The releasing of such volatiles compounds may be detected long before CI symptoms become visible.

According to some embodiments of the present invention there is provided a system with at least one sensor capable of detecting a presence or measuring concentrations of at least one volatile compound which indicates chilling stress in fruit or vegetables. Output generated by such a sensor may be received by at least one control module which performs analysis and generates output signals to effect the operation of depot conditioning system to alter storage temperature.

According to some aspects of the present invention average storage temperatures may be reduced in comparison to existing practice (by minimizing of unnecessary safety margins), relying on implementing a real-time monitoring of agricultural product quality based on detection of changes in volatile compounds produced by the agricultural product, and on a real-time response of a computerized control module governing an operation of storage conditioning system. In addition to minimizing unnecessary safety margins, systems as described above may obviate a need to use additives to prolong shelf life.

The adjustment of the temperature may include elevation of this temperature whenever detection of presence of the above mentioned volatile compound is occurred. Similarly the adjustment of the temperature may be according to changes in concentrations of the above mentioned volatile compound. For example, when a concentration of such volatile compound increases, the conditioning system would receive a command from the control module to elevate the storage temperature. According to some embodiments of the present invention the conditioning system may reduce depot temperature when there is no detection of the above mentioned volatile compound. Similarly reduction in storage temperature may be done when measurements are indicating that concentration of such a volatile compound decreases. Lowering storage temperature can prolong shelf life as long as no CI occurs.

Some aspects of the present invention include methods for prevention of post-harvest chilling injury (CI). In some cases such methods may include also processing inputs concerning detection or measuring concentrations of the aforementioned volatile compound. Such processing of input may be utilized for altering conditions in a depot where agricultural product is being stored in order to respond and adjust conditions to avoid deterioration in agricultural product quality. Altering conditions in a depot may include according to some embodiments of the above aspects, elevation of storage temperature whenever detection of presence of the above mentioned volatile compound is occurred. Similarly the adjustment of the temperature may be according to changes in concentrations of the above mentioned volatile compound. For example, when a concentration of such volatile compound increases, the conditioning system would receive a command from the control module to elevate the storage temperature. According to some embodiments of the present invention the conditioning system may reduce depot temperature when there is no detection of the above mentioned volatile compound. Similarly reduction in storage temperature may be done when measurements are indicating that the concentration of such a volatile compound decreases. According to some embodiments of the above aspects a target value for storage temperature may be set according to certain requirements such as the type of agricultural product in storage. In some examples embodying the above aspects, alteration of the storage temperature ranges between one Celsius degree below the target value to three degrees Celsius above the target value, (e.g., 10°C, 7°C, 5°C, 3°C, and 2°C).

Examples

Mango flavor and aroma are determined by the composition of the fruit volatiles and differ among cultivars. Subtropical fruit as mango is considered to be susceptive to non- optimal conditions during cold storage. Mango fruit are typically stored at 10-12 °C. It was found that concentrations of volatile constituents in mango fruit peel and pulp in various cultivars may change in response to various postharvest conditions, such as temperature, vapor treatment, methyl jasmonate (MeJA) presence, fruit fly, fruit ripening and diseases. A reduction in production of aroma volatile compounds for example in 'Kensington Pride' mango pulp was observed in response to CI.

Lipid peroxidation is a key metabolic process that is activated in response to chilling. Lipoxygenase is considered to play an important role in the peroxidation of unsaturated lipids, a possible cause of changes in membrane lipid composition, resulting in decreased membrane fluidity, membrane dysfunction and altered cellular homeostasis. Transcriptomic analysis of 'Keitt' mango fruit in response to suboptimal temperature storage revealed the activation of several pathways, including oxidation of a-linolenic acid and glycerophospholipid metabolism, resulting in lipid peroxidation. Lipoxygenase catalyzes the first step of a- linolenic acid oxidation, leading to synthesis of C₆ and C9 aldehydes. Oxylipins are a diverse class of lipid metabolites derived from the oxidation of unsaturated fatty acids that act as signaling molecules. Hydroperoxide lyase (HPL) catalyzes the cleavage of hydroperoxides to generate C₆ volatiles, also referred to as green leaf volatiles that may have a role in during plant defense signaling.

Fruit Material and Suboptimal Temperature Storage

Mango fruit (Mangifera indica L., cv. Keitt) were obtained 1-2 h postharvest from a commercial orchard (Mor Hasharon storage house, Israel), and transported (1 h) to the Agricultural Research Organization (Israel). Uniform, unblemished fruit weighing 424 ± 16 g were selected, washed with tap water and air-dried. On the same day (day of harvest), six biological replicates, each with 10 fruit, were stored at 5 °C, 8 °C, 12 °C for 19 days in the cold-storage rooms, and a further 7 days at 20 °C (shelf-life storage). The temperature in the cold-storage room was monitored by a DAQ tool (double-strand wire logger/data-acquisition control system; T.M.I. Barak Ltd., Ramat-Gan, Israel). Fruit core temperature was monitored using a MicroLite data logger LITE5032P-EXT-A (Fourier Technologies, Ramat-Gan, Israel), by inserting the probe to 5 cm depth near the fruit calyx. The experiments were repeated in three consecutive seasons— 2013, 2014 and 2015— and gave similar results. The presented experiment is of cv. Keitt in 2014.

RNA-Sequencing (RNA-Seq)

Total RNA extraction from mango fruit peel tissue, cDNA library preparation, and the RNA- Seq protocol using the Illumina Hiseq2000 system (San Diego, CA) were as described previously. The raw reads of 14 libraries were subjected to quality trimming and filtering using Trimmomatic software, sequences were mapped to a reference mango transcriptome using the Bowtie2 software alignment protocol. Abundance estimates were calculated for each mango transcript by the RSEM software package. The Bioconductor EdgeR package of the Bioconductor R packages was used to identify differentially expressed transcripts for each pair of samples, based on the count estimations for each transcript. Transcripts that were more than fourfold differentially expressed with a false discovery rate (FDR)-corrected statistical significance smaller than le-5 were considered differentially expressed. Following the Trinity protocol, expression normalization was calculated using trimmed mean of M- values (TMM), following fragments per feature kilobase per million reads mapped (FPKM) calculations. Transcripts of upregulated clusters were annotated with the Kyoto Encyclopedia of Genes and Genomes (KEGG). Upregulated transcripts with KEGG orthology descriptions were mapped to their associated KEGG pathways. Heat-mapping of upregulated genes was performed on normalized data using the R package 'FactomineR'.

Sample Preparation for GC MS Analysis

Samples were prepared by randomly slicing Mango fruit peel tissues (2 mm deep) from six fruits. Each sample was kept for 19 days in cold storage at 5 °C or 12 °C. Specimens were taken of each sample after the second day, and after days 7, 14 and 19 of the cold storage. After 19 days of cold storage the samples were stored at 20 °C. Specimens were taken after the first day and the seventh day of storage at 20 °C. This experiment was repeated for three times.. Peel tissue (2 g) of each sample and its replicates were immediately collected in a 20- mL amber vial (LaPhaPack, Langerwehe, Germany) prepared in advance with 5 mL of 20% (w/v) NaCl (Sigma-Aldrich, St Louis, MO), 0.6 g NaCl, and 50

of 10 ppm 5-2-octanol (Sigma-Aldrich) added as an internal standard. Samples were stored at -20 °C until analysis. On the day of analysis, samples were prewarmed for 1 h at 30 °C on an orbital shaker at 250 rpm.

GC MS Analysis of Mango Volatiles

A solid-phase microextraction (SPME) holder (Agilent, Palo Alto, CA) assembled with fused silica fiber (Supelco, Bellefonte, PA) coated with polydimethylsiloxane (50/30 μΜ thickness) were used to absorb the volatile compounds. Absorption and desorption of the aromatic compounds were performed on a Agilent gas chromatograph series 7890A fitted with an Agilent HP-5MS fused silica capillary column (30 mm long x 0.25 mm ID x 0.25 μιη film thickness), coupled to a 5975C MS detector (Agilent). The analytical conditions were adjusted as follows: temperature program, 40 °C for 2 min, raised at 10 °C/min to 150 °C, then at 15 °C/min to 220 °C for 5 min; injector temperature, 250 °C. Sequence total run time was 22.667 min with helium as the carrier gas adjusted to a flow rate of 0.7941 mL/min in splitless mode, with ionization energy of 70 eV. Identification and Quantification of Aroma Volatiles

Compounds were identified by use of the NIST mass spectral library (version 5) with Chemstation version E.02.00.493. The retention times of a series of straight-chain alkanes (C5-C20) (Sigma Aldrich) were used to calculate the retention indices (RIs) for all identified compounds, and the identities were confirmed by comparison of their linear RIs with the Kovats RIs of published data. Volatile compounds were semi-quantified relative to the internal standard. The concentration of volatiles was expressed as microgram per gram of peel (fresh weight). Statistical analysis

Data are presented as mean + SE and analysis involved one-way ANOVA. P < 0.05 was considered statistically significant by Tukey multiple range test with Sigma Stat 3.5 (Systat Software Inc., San Jose, CA). Principal component analysis (PCA), correlation analysis and heat-mapping for the volatile metabolites were performed using the web-based Metabo Analyst 3.0 wsv. i cj .-hti.-nai s; a; ).

Chilling Injuries and Activation of a-Linolenic Acid Metabolic Pathway 'Keitt' mango fruit were stored at various temperatures (12, 8 and 5 °C). Mango fruit stored at the commercial temperature (12 °C) showed very minor CI symptoms, whereas at 8 °C, fruit accumulated red and black spots after 2 to 3 weeks of cold storage. Storage at 5 °C led to significant accumulation of severe CI symptoms— black spots and pitting. Accumulation of those CI symptoms was correlated to severe lipid peroxidation, which was detected by malondialdehyde (MDA) accumulation and luminescence over 600 nm after 2 to 3 weeks of cold storage at 5 °C. To better understand and characterize the dynamics of transcript expression, RNA deep sequencing was conducted using Illumina HiSeq 2000 on samples extracted from the peel part of 'Keitt' mango fruit stored at 12 °C or 5 °C for 2, 7 and 14 days, as described previously. To identify chilling -related pathways that are activated during cold storage, the upregulated clusters were BLASTed against the KEGG database (http://www.genome.jp/kegg/), identified and collated to the upregulated pathways.

The α-linolenic acid-oxidation pathway was activated in mango in response to chilling stress (Figure 1). Key genes of the a-linolenic acid metabolic pathway, such as those encoding 13S- lipoxygenase (LOX), allene oxide synthase (AOS), allene oxide cyclase (AOC) and 12- oxophytodienoate reductase (OPR), were significantly upregulated at 5 °C compared to fruit on day of harvest and those stored at 12 °C. Relative expression of each transcript during fruit storage at 5 °C or 12 °C after 2, 7 and 14 days of storage in compared to fruit on day of harvest is represented in a heat map, where upregulated and downregulated genes are presented in red and green color, respectively. Most of these genes were upregulated after 2 days of cold storage at 5 °C (Figure 2).

The mango transcriptome revealed 10 LOX genes, of which 4 13S-LOX genes were upregulated. Two LOX genes— LOXi (comp20944) and LOXiv (compl7114)— were upregulated 2.1- and 4.3-fold, respectively, after 2 days of cold storage at 5 °C vs. 12 °C. LOXii and LOXiii (comp31741 and comp39918) were upregulated 2.3- and 2.5-fold, respectively, after 7 days of storage at 5 °C vs. 12 °C. Focusing on the MeJA biosynthesis pathway, downstream of LOX, three AOS isoform-encoding genes (compl 1945, comp26483, comp29600) were upregulated 4.2-, 3.1- and 4.6-fold, respectively, in response to 2 days of cold storage at 5 °C vs. 12 °C storage. AOC (compl3545) was upregulated at 5 °C vs. 12 °C at all-time points, with a maximum 9.2-fold increase after 7 days in cold storage. OPR (compl 8454) was upregulated at 5 °C vs. 12 °C at all-time points, with a maximum 2.4-fold increase after 7 days of cold storage. The results described verbatim in the above paragraph are shown visually in Figure 2. Further details appear in the table in Figure 3.

Overview of Changes in Profile of Volatile Compounds during Cold Storage

Using GC-MS, we monitored the profile of 'Keitt' mango peel volatiles at harvest, and on 2, 7, 14 and 19 days of storage at 5 °C and 12 °C. The change in volatile profile among the samples was determined by the spatial scattering of total fruit volatiles, represented by partial least squares discriminative analysis (PLS-DA). According to their spatial scattering, the samples could be divided into three distinct groups: harvest, stored at 5°C, and stored at 12°C. The results showed that the volatile profile of the 'harvest' group is very narrow and closely relates to the profile of the ' 12 °C storage' group. However, the volatile profile of the '5 °C storage' group is distinct from the other two groups. The duration of cold storage had only a minor effect on the change in total volatile profile.

Overall, 43 different putative volatiles were detected and their concentrations are presented in Figure 4A to 4E. Among these, concentrations of seventeen volatiles were significantly changed during storage at the different temperatures. It was found that nine compounds' concentrations were elevated in fruits stored at 5 °C: fZJ-3-hexenal, fZJ-3-hexenol, (E)-2- hexenal, i-hexanal, nonanal, octanal, heptanal, ortho-xylene and para-xylene, as illustrated by the right-pointing arrows. Eleven compounds' concentrations were elevated at harvest or during storage at 12 °C (copaene, ?-selinene, ?-caryophyllene, a-pinene, (5-3-carene, a- humulene, trans-3-carene-2-ol, unknown monoterpene, (Z)- ?-ocimene, a-phellandrene and terpinolene).

A correlation analysis of all 43 compounds showed strong coactivation among various monoterpenes and sesquiterpenes, among alcohols (i-butanol, 3-methyl-i-butanol and 2- methyl-i-butanol), and among the aldehydes and their alcohol derivatives (i-hexanal, (Z)-3- hexenal, (Zj-3-hexenol, (E)-2 -hexenal, nonanal and octanal).

Specific Changes in Volatiles during Cold Storage

Ten volatiles were significantly closely monitored during cold storage. Interestingly, chilling stress increased concentrations of volatiles of C₆ and C9 aldehydes and their alcohol derivatives, which are the oxidative products of the a-linolenic acid and oxylipin pathways. Compounds which were found that their concentration had significant increased at 5 °C compared to harvest and storage at 12 °C, were, i-hexanal, fZJ-3-hexenal, fZJ-3-hexenol, (E)- 2-hexenal, nonanal, heptanal and octanal. The volatiles (5-3-carene, (Z)- ?-ocimene and terpinolene were found at higher concentrations in fruit at harvest and stored at 12 °C than in fruit stored at 5 °C. As illustrated in Figure 5 the concentration of C₆ and C9 aldehydes (i- hexanal, fZJ-3-hexenal, (Zj-3-hexenol, (EJ-2-hexenal and nonanal) during 19 days of cold storage (5 °C or 12 °C) and an additional 7 days of shelf life (20 °C) showed that all of these compounds increased significantly after 2 days of cold storage at 5 °C and remained elevated until fruit transfer to 20 °C. The transfer of mango fruit to the higher temperature of 20 °C was accompanied by a sharp decrease in the concentration of those C₆ and C9 aldehydes in fruit stored previously at 5 °C and a slight increase for fruit stored previously at 12 °C.

GC-MS analysis of 'Keitt' mango fruit volatiles at harvest and during cold storage at the 12°C and sub-optimal temperature of 5 °C was made for 43 different compounds. PC A analysis showed that the overall volatile profile in fruits stored at 12 °C is similar to the volatile profile of fruits at harvest. In contrast, a significant shift in the volatile profile was observed in fruits that were stored at 5 °C. This shift seems to be mostly related to some of volatile compounds. Analysis showed that volatiles of a similar nature were coexpressed at the different temperatures, suggesting a common transcriptional regulation of those compounds. For example concentrations of several compounds— δ-3-carene, (Z)- ?-ocimene and terpinolene— which are associated with fruit ripening and with the familiar aroma and taste of the mango fruit, were lower in fruits stored at 5 °C compared to fruits stored in higher temperatures, thus indicate fruit quality deterioration as result of CI.

Lipid peroxidation is a characteristic metabolism in fruits suffering from CIs. An elevation in lipid peroxidation was observed by luminescence and MDA biochemical analysis in 'Keitt' mango fruit after 14 days of storage at 5 °C, just before the visual CI symptoms appeared. However, the transcripts in the metabolic pathway of fatty-acid oxidation of a-linolenic acid metabolism were activated after 2 days of storage at 5 °C. In this regard, the oxidation of a- linolenic acid is connected not only to fatty acid oxidation, but also to much more basic defense responses to abiotic stress— JA synthesis and oxylipin signaling— which further activated the fruit defense response. JA is a major compound regulating the global plant response to abiotic stress. JA is also known to activate chilling resistance in various fruits. LOX is a key gene in the response to chilling as it initiates the first step of a-linolenic acid oxidation and the synthesis of MeJA. It was found that four LOX transcripts were upregulated in response to chilling (Figure 2). Downstream of LOX in the JA biosynthesis pathway is AOS, which is an important enzyme in the defense response to wounding that acts as a key enzyme in oxylipin metabolism. It was found that mango AOS transcripts were activated in response to chilling (compl l945, comp26483, comp29600).

The oxidation and degradation of α-linolenic acid also lead to the release of oxylipins, such as the volatile alkenes C₆ and C₉. This reaction is mediated by HPL, which was consistently expressed during storage at 12 °C and 5 °C. The resultant C₆ and C₉ oxylipins, which are known as green leaf volatiles or oxylipins, are released mainly in response to wounding and biotic stress. Interestingly, we found by a GC-MS analysis that the same oxylipin volatiles of C₆ and C₉ alkenes (i-hexanal, (Zj-3-hexenal, fZJ-3-hexenol, (EJ-2-hexenal and nonanal) are the major upregulated compounds in response to chilling.

Transcriptomic evaluation of mango fruit peel for example suggested that storage at suboptimal temperature upregulates genes of the α-linolenic acid-oxidation pathway which leads to synthesis of C₆ and C₉ aldehydes before CI symptoms become visible as demonstrated in gas chromatography-mass spectrometry (GC-MS) analysis of the volatile profile of mango fruit peel. Thus, a presence of oxylipin volatiles of C6 and C9 aldehydes, may serve according to aspects of the present invention as signals which indicate a beginning of metabolisms which are associated with CI and/or deterioration of fruit quality. Such an early indication may be utilized for monitoring CI and/or fruit quality and for real-time adjustment of storage conditions.

Claims

1. A system for prevention of post-harvest chilling injury (CI), said system comprising at least one sensor capable of detecting a concentration of at least one volatile compound, wherein said volatile compound indicates said CI.

2. The system of claim 1, wherein said at least one volatile compound is at least one alkene.

3. The system of claim 1, wherein said at least one volatile compound is at least one oxylipin.

4. The system of claim 1, wherein said at least one volatile compound is selected from the group consisting of 7-hexanal, Z -3-hexenal, Z -3-hexenol, (¾)-2-hexenal, nonanal, heptanal, octanal.

5. The system of claim 1, wherein said agricultural product is selected from the group consisting of mango, pomegranate, avocado, citrus, lattice, pepper, apple, pear, cherry, peach, grape, banana, and tomato.

6. The system of claim 5, wherein said agricultural product is mango.

7. The system of claim 1, further comprising at least one module capable of controlling the operation of a conditioning system in a depot, wherein said controller receives and processes input from said sensor.

8. A method for prevention of post-harvest chilling injury (CI), said method comprising detecting a presence or measuring concentrations of at least one volatile compound, wherein said at least one volatile compound indicates for said CI.

9. The method of claim 8, wherein said crop is selected from the group consisting of mango, pomegranate, avocado, citrus, pepper, apple, pear, cherry, peach, grape, banana, and tomato.

10. The system of claim 1, wherein said at least one volatile compound is at least one oxylipin.

11. The system of claim 1, wherein said at least one volatile compound is selected from the group consisting of 7-hexanal, Z -3-hexenal, Z -3-hexenol, (¾⁾-2-hexenal, nonanal, heptanal, octanal.

12. The method of claim 9, wherein said crop is mango.

13. The method of claim 8, said method further comprising:

receiving and processing input concerning said detecting and/or said measuring;

altering conditions in a depot according to said processing.

14. The method of claim 13, wherein said altering comprises altering a temperature in a depot.

15. The method of claim 14, wherein said altering temperature comprises elevating said temperature whenever said detecting of a presence of at least one volatile compound, is occurring.

16. The method of claim 14, wherein said altering of temperature comprises elevating said temperature in a depot whenever said measuring indicates increase in said concentration.

17. The method of claim 14, wherein said altering temperature further comprises reducing said temperature whenever said measuring indicates reduce of said concentration of at least one volatile compound.

18. The system of claim 15, wherein said altering temperature, further comprises reducing said temperature whenever said presence of at least one volatile compound drops below a threshold level.

19. The method of claim 14, wherein further comprises setting a target value for said temperature, wherein said altering temperature ranges between one Celsius degree below said target value to three degrees Celsius above said target value.

20. The method of claim 19, wherein said target value selected from the group consisting of 10°C, 7°C, 5°C, 3°C, and 2°C.

21. The method of claim 20, wherein said crop is mango, and wherein said temperature target value is 10°C.