Postharvest L-phenylalanine Application on Shelf life and Physicochemical Characteristics of Sabrina Strawberry During Cold Storage

Abstract

Introduction One of the most important global challenges is food waste, about 30% of the world's agricultural land is wasted. Every year, about 9.5 million tons of food is lost in the post-harvest phase of agriculture. Therefore, storage technology is very important to increase shelf life, preserve nutrition and maintain the taste of fresh products. Storing strawberry fruits at an inappropriate temperature after harvesting significantly increases weight loss, rotting and softening. L-phenylalanine as an amino acid is used for the biosynthesis of all phenolic compounds through the phenylpropanoid pathway. In recent years, the application of exogenous phenylalanine has been considered for use as a biologically safe molecule to maintain the postharvest quality of many horticultural crops. L-phenylalanine treatment has been reported to reduce the frost damage of plum fruit during cold storage by maintaining membrane integrity and improving reactive oxygen species (ROS) scavenging capacity. The treated fruit showed a higher DPPH inhibition capacity by increasing the accumulation of phenolic compounds and antioxidant enzyme activity. Aghdam et al. (2019) also reported that application of L-phenylalanine significantly reduced cold damage, membrane lipid peroxidation and ROS accumulation in tomato fruits during cold storage. Materials and Methods Strawberry fruits were obtained from a commercial greenhouse located in Urmia at full maturity stage. The fruits were transported to the laboratory of the Department of Horticultural Sciences in Urmia University with necessary precautions to prevent any mechanical damage to the product. The fruits were separated in terms of size and uniformity, so that the fruits were divided into 3 groups, one group as a control group and 2 groups were treated with concentrations of L-phenylalanine (4 and 8 mM). After drying the treated fruits, they were placed in zipped nylon bags and kept in a cold room for 15 days at a temperature of 3 ± 0.5 °C and a relative humidity of 90-95%. Also, three biological replicates at each time point were included in the analysis. The samples obtained at each of these times were used to evaluate skin color, titratable acidity, soluble solids, taste index, pH, weight loss, firmness, antioxidant capacity, total phenol content, and polyphenol oxidase enzyme activity. Results and Discussion The results showed that the effect of post-harvest treatment, storage time, and the interaction between them were statistically significant on all of the traits. In terms of color changes, the effect of post-harvest treatment (p≤0.05) was significant only in b* index, and the highest rate was observed in the 4 Phe treatment. The effect of storage time was also significant in a* and Chroma indices (p≤0.05) and the highest level was observed in both of these indices at day 5. The effect of storage time was also significant in TA (p≤0.01), the highest value was observed in day 10. In antioxidant capacity (p≤0.05), TSS (p≤0.05) and taste index (p≤0.01), the interaction effect between storage time and Phe treatment was significant. In antioxidant capacity, the highest percentage of DPPH inhibition was observed in day 10 and 4 Phe treatment, in TSS, the highest rate was observed on day 10 and 8 Phe treatment, and in taste index, the highest rate was observed on day 15 and 4 Phe treatment. The effect of post-harvest Phe treatment and storage period on fruit weight loss was significant (p≤0.05) and (p≤0.01) respectively, and the lowest percentage of weight loss was observed in Phe 4 and day 5. In terms of firmness and total phenol content, only the effect of Phe treatment was significant (p≤0.05) and (p≤0.01), respectively, the highest level of firmness in the 4 Phe treatment and the highest amount of total phenol content in the 8 Phe treatment were observed. In the PPO enzyme, only the effect of storage time (p≤0.05) was significant. Conclusion According to the obtained results, the 4 Phe treatment is the best concentration of phenylalanine to increase the shelf life of harvested strawberry fruits under cold storage.

Keywords

• amino acid
• fruit firmness
• titratable acid
• total phenol