Effects of Reactive Oxygen Levels on Chilling Injury and Storability in 21 Apricot Varieties from Different Production Areas in China.

The key factors for resistance to chilling injury in apricot fruits were obtained by analyzing the low-temperature storage characteristics of 21 varieties of apricot fruits in the main producing areas of China. Twenty-one varieties of apricots from different production areas in China were stored at 0 °C for 50 d and then shelved at 25 °C. The storage quality, chilling injury, reactive oxygen species (ROS), antioxidant ability, and contents of bioactive substances of the apricots were measured and analyzed. The results showed that the 21 varieties of apricot fruits could be divided into two categories according to tolerance during low-temperature storage, where there was chilling tolerance and lack of chilling tolerance. Eleven varieties of apricots, of which Xiangbai and Yunbai are representative, suffered from severe chilling injury after cold storage and shelf life. After 50 d of storage at 0 °C, the levels of superoxide anions and hydrogen peroxide accumulated in the 11 varieties of apricots with a lack of chilling tolerance during storage were significantly higher than those in the remaining 10 varieties of apricots with chilling tolerance. In addition, the activities of ROS scavenging enzymes, represented by superoxide dismutase, catalase and peroxidase, were significantly decreased in 11 varieties of apricots with a lack of chilling tolerance during storage. The contents of bioactive substances with ROS scavenging ability, represented by ascorbic acid, total phenols, carotenoids, and total flavonoids, also significantly decreased. The 10 varieties of apricots, of which Akeximixi and Suanmao are representative, were less affected by chilling injury because the production and removal of ROS were maintained at normal levels, avoiding the damaging effects of ROS accumulation in the fruit. In addition, the 10 apricot varieties with chilling tolerance during storage had higher sugar and acid contents after harvest. This could supply energy for physiological metabolism during cold storage and provide carbon skeletons for secondary metabolism, thus enhancing the chilling tolerance of the fruits. Based on the results of cluster analysis combined with the geographical distribution of the 21 fruit varieties, it was found that apricot varieties with chilling tolerance during storage were all from the northwestern region of China where diurnal temperature differences and rapid climate changes occur. In conclusion, maintaining the balance of ROS production and removal in apricots during cold storage is a key factor to enhance the storage tolerance of apricots. Moreover, apricots with higher initial glycolic acid and bioactive substance contents are less susceptible to chilling injury.

Comparative Study on the Volatile Organic Compounds and Characteristic Flavor Fingerprints of Five Varieties of Walnut Oil in Northwest China Using Using Headspace Gas Chromatography-Ion Mobility Spectrometry.

Odor is an important characteristic of walnut oil; walnut oil aromas from different varieties smell differently. In order to compare the differences of volatile flavor characteristics in different varieties of walnut oil, the volatile organic compounds (VOCs) of walnut oil from five different walnut varieties in Northwest China were detected and analyzed using headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS). The results showed that 41 VOCs in total were identified in walnut oil from five different varieties, including 14 aldehydes, 8 alcohols, 4 ketones, and 2 esters. Walnut oil (WO) extracted from the "Zha343" variety was most abundant in VOCs. The relative odor activity value (ROAV) analysis showed that aldehydes were the main aroma substances of walnut oil; specifically, hexanal, pentanal, and heptanal were the most abundant. Fingerprints and heat map analysis indicated that WO extracted from the "Xin2", "185", "Xin'guang", and "Zha343" varieties, but not from the "Xinfeng" variety, had characteristic markers. The relative content differences of eight key VOCs in WO from five varieties can be directly compared by Kruskal-Wallis tests, among which the distribution four substances, hexanal (M), hexanal (D), pentanal (M), (E)-2-hexanal (M), presented extremely significant differences (P<0.01). According to the results of the principal component analysis (PCA), WO extracted from the "Zha343" variety was distinct from the other four varieties; in addition, WO extracted from the "Xin2" variety exhibited similarity to WO extracted from the "185" variety, and WO extracted from the "Xinfeng" variety showed similarity to WO extracted from the "Xin'guang" variety. These results reveal that there are certain differences in the VOCs extracted from five different WO varieties, making it feasible to distinguish different varieties of walnut oil or to rapidly detect walnut oil quality based on its volatile substances profile.

Near-freezing temperature storage improves shelf-life and suppresses chilling injury in postharvest apricot fruit (Prunus armeniaca L.) by regulating cell wall metabolism.

To avoid chilling injury (CI) of apricots during storage, 1-2 °C and 4-6 °C storage as controls, the relationship between changes in cell wall characteristics and the occurrences of chilling injury under near-freezing temperature (NFT) storage was studied. NFT-stored improved apricots quality and inhibited CI index, membrane permeability and malondialdehyde (MDA) content; This also significantly inhibited the activity of cell wall modifying enzymes, delaying the solubilization of water-soluble pectin (WSP) and the degradation of cellulose. Transmission electron microscopy (TEM) imaging revealed that the density of the middle lamella in stored for 49 d was higher NFT than controlled temperature, delaying cell wall and chloroplast disintegration. Additionally, NFT-stored has no CI during the shelf life, and can be normal after ripening, maintaining higher commodity rate and sensory characteristics. These conclusions show that NFT storage can effectively improve the cold resistance of apricot fruit.

Methyl salicylate affects the lipophilic and hydrophilic antioxidant capacities of apricot by regulating carotenoid biosynthesis and phenolic metabolism.

The carotenoid biosynthesis and phenolic metabolism were studied to explain the effect of methyl salicylate (MeSA) on the lipophilic antioxidant capacity (LAC) and hydrophilic antioxidant capacity (HAC) in apricot during postharvest storage. Our results indicated that the HAC of apricot was higher than LAC and mainly responsible for total antioxidant capacity of apricot. Preharvest spraying of MeSA (0.2 mmol L-1) could improve the value of HAC but declined LAC of apricot. The enhanced HAC in MeSA treated apricot was positively related to the increased content of phenolics, especially to (+)-catechin, which was catalyzed by the enzymes related to phenolic metabolism. While, the decline of LAC in apricot treated by MeSA could be attributed to the inhibition of carotenoids accumulation, which was regulated by carotenogenic genes. We concluded that MeSA could affect the lipophilic and hydrophilic antioxidant capacity of apricot by regulating carotenoid biosynthesis and phenolic metabolism.

Epsilon-poly-l-lysine (ε-PL) exhibits multifaceted antifungal mechanisms of action that control postharvest Alternaria rot.

ε-Poly-l-lysine (ε-PL) is a natural antimicrobial poly-cationic peptide widely applied as a natural preservative in the food industry, whereas its application in preventing postharvest loss of fruit was largely absent. This study investigated the antifungal activity of ε-PL and determined the possible mechanisms involved. The in vivo results indicated that 500 mg L-1 exogenous ε-PL treatment significantly inhibited black spot rot in apple, jujube, and tomato. The lesion diameter inhibition rate was range from 20.11% to 29.09% by 500 mg L-1 ε-PL treatment. ε-PL exerts antifungal activity against A. alternata in vitro, the half-inhibition concentration is 160.1 mg L-1. ε-PL induced morphology and ultrastructure change on the pathogen, which resulted in the inhibition of A. alternata. This was accomplished by disturbing pathogen membrane integrity and functionality. The fluorometric assay confirmed that ε-PL induced endogenous reactive oxygen species formation and accumulation in A. alternata and the elicited severe lipid peroxidation that caused membrane lesions. Further, ε-PL treatment enhanced the expression of genes involved in antioxidant metabolism and pathogenesis-related responses in apple fruit. These findings illustrated that ε-PL exhibits multifaceted antifungal activity by the direct effect on the pathogen as well as induce host defense responses. ε-PL may be conducive as a promising alternative for Alternaria rot management.

Impact of near freezing temperature storage on postharvest quality and antioxidant capacity of two apricot (Prunus armeniaca L.) cultivars.

To reduce the postharvest loss and improve apricot quality attributes, near freezing temperature (NFT) technology was applied to store apricot cultivars (var. "Xiaobai" and "Daliguang"). The NFT storage temperatures for the "Xiaobai" apricot and "Daliguang" apricot were determined as -1.9 to -2.3°C and -1.2 to -1.6°C, respectively. Storage at NFT significantly improved the storage quality of apricots by suppressing respiration rate, ethylene production, decay rate, internal browning index, membrane permeability, and malondialdehyde content. Apricots stored at NFT maintained higher firmness, total soluble solids, titrable acid, total phenolics, total flavonoids, and ascorbic acid content than those stored at 0-1°C. Additionally, NFT storage enhanced the capacity of radical scavenging and metal chelating, antioxidant properties in apricots compared to those stored at 0-1°C. Hence, NFT storage proved to be an effective method to improve the quality and antioxidant attributes of apricots. PRACTICAL APPLICATIONS: This study explored the effect of storage at near freezing temperature (NFT) on the postharvest quality of two cultivars of apricot (var. "Xiaobai" and "Daliguang"). We found that storage for 70 days at NFT resulted in better edible quality compared to storage at 0-1°C and 4-6°C. Apricot quality was determined in terms of respiration rate, ethylene production, decay rate, internal browning index, membrane permeability, malondialdehyde content, firmness, total soluble solids, titrable acid, total phenolics, total flavonoids, and ascorbic acid content. The antioxidant properties of the fruits were also retained during storage at NFT. We believe that our study makes a significant contribution to the preservative industry because it demonstrates the superiority of NFT storage over low temperature for apricots.

Near-freezing temperature storage enhances chilling tolerance in nectarine fruit through its regulation of soluble sugars and energy metabolism.

To avoid chilling injury (CI) of nectarines during storage, the impact of near-freezing temperature (NFT) (-1.4 ±â€¯0.1 °C), 0 ±â€¯0.1 °C and 5 ±â€¯0.1 °C on CI incidence, ion leakage, levels of soluble sugars and enzymatic activities related to soluble sugars and energy metabolism, were investigated over five weeks. NFT-stored fruit showed no CI symptoms and significantly (P < 0.05) lower increase of ion leakage than those kept at 0 and 5 °C. NFT significantly (P < 0.05) diminished the activities of sucrose metabolism-associated enzymes leading to a higher level of sucrose in fruit, and maintained higher activities of hexokinase and fructokinase. Additionally, NFT-stored fruit exhibited significantly (P < 0.05) higher activities of energy metabolism-associated enzymes than fruit stored at 0 and 5 °C, leading to high levels of adenosine triphosphate and energy in fruit. These results indicated that NFT storage can effectively enhance chilling tolerance of nectarine fruit by inducing the metabolism of soluble carbohydrates and energy.

Thermal death kinetics of fifth-instar Corcyras cephalonica (Lepidoptera: Galleriidae).

The infestation of rice moth, Corcyras cephalonica (Lepidoptera: Galleriidae), causes severe losses in postharvest walnuts. Heat has been studied as a phytosanitary treatment to replace chemical fumigation for controlling this pest. Information on kinetics for thermal mortality of C. cephalonica is needed for developing effective postharvest phytosanitary thermal treatments of walnuts. Thermal death kinetics of fifth-instar C. cephalonica were investigated at temperatures between 44°C and 50°C at a heating rate of 5°C min(-1) using a heating block system. The results showed that thermal-death curves for C. cephalonica larvae followed a 0 order of kinetic reaction. The time to reach 100% mortality decreased with increasing temperature from 150 min at 44°C to 2.5 min at 50°C. The activation energy for controlling C. cephalonica was 466-592 kJ/mol, and the z value obtained from the thermal death time curve was 3.3°C. This kinetic model prediction could be useful in designing the thermal treatment protocol for controlling C. cephalonica in walnuts.