Natamycin treatment reduces the quality changes of postharvest mulberry fruit during storage

Activity and safety evaluation of natural preservatives

Synthetic preservatives are widely used in the food industry to control spoilage and growth of pathogenic microorganisms, inhibit lipid oxidation processes and extend the shelf life of food. However, synthetic preservatives have some side effects that can lead to poisoning, cancer and other degenerative diseases. With the improvement of living standards, people are developing safer natural preservatives to replace synthetic preservatives, including plant derived preservatives (polyphenols, essential oils, flavonoids), animal derived preservatives (lysozyme, antimicrobial peptide, chitosan) and microorganism derived preservatives (nisin, natamycin, ε-polylysine, phage). These natural preservatives exert antibacterial effects by disrupting microbial cell wall/membrane structures, interfering with DNA/RNA replication and transcription, and affecting protein synthesis and metabolism. This review summarizes the natural bioactive compounds (polyphenols, flavonoids and terpenoids, etc.) in these preservatives, their antioxidant and antibacterial activities, and safety evaluation in various products.

An Aquaporin Gene (KoPIP2;1) Isolated from Mangrove Plant Kandelia obovata Had Enhanced Cold Tolerance of Transgenic Arabidopsis thaliana

Aquaporins (AQPs) are essential channel proteins that play central roles in maintaining water homeostasis. Here, a novel aquaporin gene, named KoPIP2;1, was cloned from the mangrove plant Kandelia obovata by RACE technology. The KoPIP2;1 gene was 1404 bp in length with an open reading frame (ORF) of 852 bp, encoded with 283 amino acids. Database comparisons revealed that KoPIP2;1 protein shared the highest identity (91.26%) with the aquaporin HbPIP2;2, which was isolated from Hevea brasiliensis. Gene expression analysis revealed that the KoPIP2;1 gene was induced higher in leaves than in stems and roots of K. obovata under cold stress. Transient expression of KoPIP2;1 in Nicotiana benthamiana epidermal cells revealed that the KoPIP2;1 protein was localized to the plasma membrane. Overexpressing KoPIP2;1 in Arabidopsis significantly enhanced the lateral root number of the transgenic lines. KoPIP2;1 transgenic Arabidopsis demonstrated better growth, elevated proline content, increased superoxide dismutase (SOD) and peroxidase (POD) activities, and reduced malondialdehyde (MDA) content compared with the wild-type Arabidopsis when exposed to cold stress. The findings suggest that overexpression of KoPIP2;1 probably conferred cold tolerance of transgenic Arabidopsis by enhancing osmoregulation and antioxidant capacity. This present data presents a valuable gene resource that contributes to the advancement of our understanding of aquaporins and their potential application in enhancing plant stress tolerance.

Control Efficacy of Salicylic Acid Microcapsules against Postharvest Blue Mold in Apple Fruit

Salicylic acid (SA) is a natural inducer of disease resistance in fruit, but its application in the food industry is limited due to low water solubility. Here, SA was encapsulated in β-cyclodextrin (β-CD) via the host-guest inclusion complexation method, and the efficacy of SA microcapsules (SAM) against blue mold caused by Penicillium expansum in postharvest apple fruit was elucidated. It was observed that SAM was the most effective in inhibiting the mycelial growth of P. expansum in vitro. SAM was also superior to SA for control of blue mold under in vivo conditions. Enzyme activity analysis revealed that both SA and SAM enhanced the activities of superoxide dismutase (SOD) and phenylalanine ammonia lyase (PAL) in apple fruit, whereas SAM led to higher SOD activities than SA. Total phenolic contents in the SAM group were higher than those in the SA group at the early stage of storage. SAM also improved fruit quality by retarding firmness loss and maintaining higher total soluble solids (TSS) contents. These findings indicate that microcapsules can serve as a promising formulation to load SA for increasing P. expansum inhibition activity and improving quality attributes in apple fruit.

Effects of resveratrol treatment on quality and antioxidant properties of postharvest strawberry fruit

Strawberry fruit is one of people's favorite fruits. It has high nutritional value and health care effects. Strawberries lose their edible value quickly after being picked because of their thin skin, which is easily damaged. In order to find a method to maintain the quality of strawberries, the effects of resveratrol treatment on the nutritional quality and antioxidant metabolism of strawberry fruit were studied. The result indicated that 100 μM resveratrol was the optimal concentration to delay the occurrence of decay. Strawberry fruit treated with resveratrol delayed the decrease in firmness, total soluble solids (TSS), total phenolics content (TPC), total flavonoid content (TFC), vitamin C (Vc) content,1,1-diphenyl-2-picrylhydrazyl (DPPH), and 2,2'-azino-bis (3-ethylbezothi- azot-hiazoline-6-sulfonic acid) (ABTS) radical scavenging capacities. The malondialdehyde (MDA) content, hydrogen peroxide (H₂ O₂ ) content, and superoxide anion (O₂ ^•- ) production of control fruit were significantly higher than those of treated fruit. Strawberry fruit treated with resveratrol also increased the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) during storage. Therefore, resveratrol has been proved to effectively improve the nutritional quality and antioxidant properties of strawberry fruit. PRACTICAL APPLICATIONS: Strawberry fruit is rich in nutrients, which is beneficial to human health. But strawberry fruit has high water content and soft tissue, which is easy to be damaged and decayed. Therefore, it is particularly important to find a way to maintain strawberry fruit quality. In this study, resveratrol has good antioxidant, health care, and antibacterial properties. Resveratrol treatment can maintain the nutritional quality of strawberry fruit and can be used as an effective method for strawberry fruit preservation.

Natamycin: a natural preservative for food applications-a review

Natamycin is a natural antimicrobial peptide produced by the strains of Streptomyces natalensis. It effectively acts as an antifungal preservative on various food products like yogurt, khoa, sausages, juices, wines, etc. Additionally, it has been used as a bio preservative and is listed as generally recognized as a safe ingredient for various food applications. In this review, natamycin properties, production methods, toxicity, and application as a natural preservative in different foods are emphasized. This review also focuses on optimal condition and process control required in natamycin production. The mode of action and inhibitory effect of natamycin on yeast and molds inhibition and its formulation and dosage to preserve various food products, coating, and hurdle applications are summarized. Understanding the scientific factors in natamycin's production process, its toxicity, and its efficiency as a preservative will open its practical application in various food products.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-021-00981-1.

Influence of hot water treatment and O-carboxymethyl chitosan coating on postharvest quality and ripening in Hami melons (Cucumis melo var. saccharinus) under long-term simulated transport vibration

Hami melon (Cucumis melo var. saccharinus) is famous in China because of its delicious taste. The fast post-harvest metabolism of Hami melon, which is harvested in summer, creates challenges for preservation during storage. In this study, the ripening-related changes in Hami melon were monitored throughout postharvest storage, including transport. The effects of hot water (HW) treatment and HW treatment in combination with O-carboxymethyl chitosan (CMC) coating on ripening were evaluated based on the changes in membrane leakage; respiration rates; malondialdehyde (MDA) content; superoxide dismutase, catalase, and peroxidase activities; total antioxidant capacity (TAC); and total phenolic content during storage. Transmission electron microscopy and magnetic resonance imaging were also used to monitor changes in the quality of Hami melons during storage. The results indicate that transport vibration can accelerate ripening-related changes in Hami melon. Transport vibration increased membrane leakage and microstructural changes in the melon tissue; enhanced the respiration rate and MDA content; suppressed the activities of antioxidant enzymes; and decreased the TAC and total phenolic contents. Compared to HW treatment alone, HW treatment combined with the coating with 1% (w/v) CMC more effectively delayed the ripening-related changes in Hami melons under transport vibration. PRACTICAL APPLICATIONS: The results of this study show that transport vibration can accelerate ripening in Hami melons. Both hot water (HW) treatment and a combination of HW treatment and O-carboxymethyl chitosan (CMC) coating were effective in delaying ripening in Hami melons under simulated long-term transport vibration. Compared with HW treatment alone, HW treatment combined with CMC coating was more effective in preserving Hami melons, as indicated by lower respiration rates; better integrity of the plasma membrane and cell wall in the parenchyma tissue; lower membrane leakage and malondialdehyde content; greater antioxidant enzyme activities, total antioxidant capacity, and total phenolic content; and improved magnetic resonance imaging T₂ relaxation values. Thus, HW treatment combined with CMC coating provides a useful way for the Hami melon industry to maintain postharvest quality, extend the shelf life, and improve the marketing of Hami melon.