A combination of heat-shock treatment and edible coating application could extend the shelf life of blueberries by 7?14 d

The quality of blueberry fruit is easily altered after harvest. We investigated the regulatory mechanism of heat-shock (postharvest treatment) and edible coating (preharvest treatment) on the post-harvest physiological quality of blueberry from the perspective of physiological, biochemical and organoleptic characteristics. In our research, the optimal TKL concentration and the appropriate range of heat-shock temperatures were first screened based on actual application results, and then a combination of heat-shock temperature and TKL coating with significant differences in preservation effects was selected to investigate the effects of different heat-shock temperatures and TKL60 composite coating on post-harvest quality and volatile compound concentration of blueberries under refrigerated conditions. Our results showed that TKL with 60 mg/L thymol can retard the development of the degree of membrane lipid peroxidation and effectively reduce the incidence of fruit decay and the severity of blueberries infected with major pathogens at 25 ?C. Meanwhile, heat-shock treatments were effective in maintaining the quality of blueberries, with a certain advantage from 45 ?C to 65 ?C after 8 d of storage at ambient temperature, but these treated groups were slightly inferior to TKL60 groups for fresh-keeping effect. Remarkably, the combination of heat-shock treatment and edible coating application could extend the shelf life of blueberries by 7?14 d compared to the results obtained with coating alone under low temperature storage. Specifically, heat treatment at 45 ?C for 60 min after TKL60 coating (HT2) retarded the decrease in the levels of ascorbic acid, total anthocyanin, total acid and soluble solids. Gas chromatography?mass spectrometry hierarchical clustering analysis showed that this treatment also improved the aroma of the fruit, which maintained a certain similarity with that of fresh blueberries after 14 d. Principal component analysis (PCA) of the results of the evaluations carried out using an electronic nose (E-nose) and electronic tongue (E-tongue) showed that blueberries of the HT2 treated group did not show a large placement change of the PC1 distribution area from that of the fresh and blank control group. Accordingly, the combination of coating with heat-shock treatment can effectively improve the post-harvest quality and aroma compound concentration of blueberries, showing good application potential in storage and preservation of fresh fruits such as blueberries. The text before is the Abstract of the article IntroductionWith the increasing income and consumption levels of consumers, blueberries have increased in popularity due to their health benefits, nutritional value, and taste [1,2]. However, blueberry harvesting season is always hot and rainy (in southwest China), so blueberries are very perishable after picking, making the fruit intolerant to storage and reducing its commercial value. Therefore, there is an urgent need to identify effective preservation methods that can extend the shelf life of blueberry.Several preservation methods are commonly used to improve the shelf life of blueberry, including:- low temperature storage [3], - controlled-atmosphere (CA) techniques [4], - irradiation treatment [5], - essential oil fumigation [6], - heat-shock treatment [7], and - edible film coating [8]. Low-temperature storage delays senescence and helps to preserve fruit quality [9]. However, this preservation method is the most basic and is often applied in combination with other preservation methods in practice. CA can reduce blueberry respiratory metabolism, slowing down senescence [10]. Tina, et al. [11] conclude that the optimal controlled atmosphere under long-term storage is 5% CO2, 5% O2, and 90% N2 for the maintenance of weight and nutritional quality of the blueberry fruit ?Liberty?. However, the sudden change of atmosphere could elicit a physical abiotic stress response in the fruit, negatively affecting quality. Irradiation treatment significantly reduced total aerobic bacteria and yeast on the fruit surface [12]. Villagra et al. [13] showed that UV-C irradiation could be an interesting tool to improve antioxidant potential in highbush blueberries, which can negatively affect fruit quality for fresh consumption. The essential oils carvacrol, anethole, cinnamaldehyde, cinnamic acid, perillaldehyde, linalool, and p-cymene can inhibit blueberry decay, with carvacrol, anethole, and perillaldehyde simultaneously enhancing antioxidant activity of the fruit [14]. However, essential oil fumigation had significant negative effects on several sensory attributes such as sourness, astringency, juiciness, bitterness, and blueberry-like flavor [6]. As a barrier against water and oxygen exchange, mechanical damage, and pathogen infection, edible coatings are widely used to maintain quality and prolong the shelf life of horticultural products [15]. A pullulan coating can reduce the number of bacteria and mold in blueberry fruit, delay fruit ripening, and reduce weight loss [16]. Previous studies have found that a thymol/Konjac glucomannan (KGM)/low acyl gellan gum (LAG) (TKL) coating can reduce the secondary damage of postharvest treatment to fruit, effectively improve the edible quality of blueberry and prolong the storage period [17]. Heat-shock treatment refers to a physical preservation method for postharvest fruits and vegetables in a short period under non-lethal high temperatures [18]. Hot water at 42 ?C reduces the decay of kiwifruit caused by Botrytis cinerea during postharvest storage and resulted in lower malondialdehyde content and higher total phenolic content in kiwifruits, regardless of whether it was used together with 5 g/L (w/v) potassium sorbate [19]. Hot air combined with nanomaterial packaging effectively inhibited respiratory intensity and delayed the senescence of bayberries [20]. Fan et al. found that hot water treatment at 22, 45, 50, or 60 ?C increased the commodity rate of blueberries after four weeks of storage [7]. This is similar to the results of our pre-experiment. However, studies have shown that the combination of heat-shock and coating treatment is more effective in maintaining fruit quality [21,22]. The materials used in heat-shock (HT) treatment and TKL coating technology are simple and low cost. In addition, the combination of HT treatment and TKL (*) coating technology can increase the release of effective components in the coating and inhibit or kill pathogenic microorganisms. HT treatment can also soften blueberry epidermal wax, plug fruit epidermal pores, and slow down respiration, extending the storage period of blueberry. To the best of our knowledge, there is no available scientific literature on the use of edible coatings in combination with heat treatment to maintain the quality and extend the shelf life of blueberries. Therefore, the aim of the present study was to evaluate the effect of a combined treatment using TKL edible coating and HT on freshness preservation, flavor compounds, and physiological?biochemical parameters of blueberry. (*) One of the items of the content is the process of fabrication of TKL coating; link to the original paper is available below. Picture is Fig 6 of the original paper, Figure 6. Flavor characterizations of HT in blueberries during storage times at 2 ?C (n = 3); (a,b) represent PAC of taste and odor fingerprint profile, respectively; (c) represents aroma components; (d) represents hierarchical clustering analysis. SourceUse of Heat-Shock and Edible Coating to Improve the Postharvest Preservation of BlueberriesChunyan Liu, Jie Ding, Peng Huang ,Hongying Li,Yan Liu,Yuwei Zhang, Xinjie Hu, Shanggui Deng, Yaowen Liu & Wen Qin?Foods 2023, 12(4), 789; https://doi.org/10.3390/foods12040789https://www.mdpi.com/2304-8158/12/4/789