Strawberries are widely known for their rapid spoilage and deterioration. To address this, significant research has focused on various preservation methods, including quick-freezing, refrigeration, ambient storage, heat treatment, modified atmosphere packaging, radiation treatment, and coating technologies. However, many of these methods are either too costly or too complex for ordinary farmers to adopt.
In response to the economic losses and food safety concerns associated with fruit spoilage, recent years have seen the development of eco-friendly pesticides based on oligosaccharides. These are derived from biological resources and are used to prevent diseases in food crops, economic plants, and other vegetation. They are efficient, safe, non-toxic, and do not lead to plant resistance. Chito-oligosaccharides, in particular, offer several advantages such as good pest resistance, safety, minimal required doses, high efficiency, and low cost. They can increase the yield of fruits, vegetables, and grains by 10%-30% and can partially replace chemical pesticides in biopesticide products. Given their effect on post-harvest fruits and vegetables and their broad applicability to plant health, chito-oligosaccharides are poised to become a leading product for the next generation.
To find strawberry preservation methods suitable for ordinary farmers, our research focused on the effectiveness of Chito-oligosaccharides (COS) in preserving strawberries and their impact on the fruit’s quality.
Check out our COS in this experiment.
What is Chito-oligosaccharide
Chito-oligosaccharide, also known as β-1,4-oligosaccharide glucosamine, is a product of chitosan degradation, consisting of 2 to 20 glucosamine units connected by β-1,4-glycosidic bonds. Chitin, found in the cell walls or membranes of fungi, marine animals, and yeasts, is abundant, second only to cellulose in quantity. Chitosan, obtained by deacetylating chitin, is a natural biomaterial widely used in agriculture.
We find out that chito-oligosaccharides stand out for their potential in sustainable agriculture, not only as an effective method for preserving strawberries but also for their broader implications in enhancing crop yield and reducing reliance on chemical pesticides.
Chitosan oligosaccharide (COS) is distinguished by its abundant raw material sources and low production costs, making it one of the most successfully utilized oligosaccharides to date. Research into the functionality and mechanisms of COS in plant physiological activity has revealed its roles in plant growth regulation (including inducing resistance), antimicrobial activity (bactericidal and bacteriostatic effects), enhancing insecticidal activity, and repellency.
As a natural plant growth regulator, COS significantly affects plant growth, seed germination rates, and root development of crops, while also improving crop quality and yield. Studies have shown that the specific structure of COS is active and can stimulate plant resistance at low concentrations, suggesting the existence of COS-specific receptors in plants and that COS binds to plant cells with specificity and selectivity.
COS has been widely applied to various plants, such as wheat, rapeseed, tobacco, tomatoes, pears, and citrus. Interestingly, COS has been found to increase the polyphenol content in oregano and enhance the levels of Vitamin C and polyphenols in cherries. These findings imply that COS not only acts as an effective plant immune regulator to combat disease but also influences the quality of fruits and vegetables by affecting the content of secondary metabolites.
Numerous studies suggest that COS treatment can affect the ripening and softening of apricots, cherries, strawberries, and citrus fruits. These studies mainly focus on COS-induced disease resistance and maintaining fruit quality, with few reports on the mechanism of COS in preserving freshness.
Chitosan oligosaccharide (COS)’s Concentration Setting
Based on preliminary experiments, concentrations of 50mg/L and 100mg/L of COS were determined to be the most effective. Thus, these concentrations were selected for experiments.
Strawberries chosen for the study were strictly selected to ensure no damage or decay and consistent freshness, with a maturity level of approximately 70%. Each group of strawberries consisted of 45 pieces, with 15 pieces reserved for quality measurements after five days. The strawberries were then soaked for 1 minute at the set concentrations, drained, and air-dried.
The Effect of Chitosan Oligosaccharide on Strawberry Firmness
Different Group’s Chitosan Oligosaccharide Influence on Strawberry Firmness
The firmness of fruit significantly influences the appearance and texture of strawberries, with a decrease in firmness during storage primarily due to the loss of cell wall-related substances. As such, firmness is a crucial indicator of fruit softening, making it a key measure for determining if the fruit has undergone excessive softening.
The image shows that, with increasing days of storage, the firmness of strawberries generally decreases. However, groups treated with 50 mg/L and 100 mg/L concentrations of Chitosan Oligosaccharide (COS) showed a delay in the reduction of firmness compared to the control group. Notably, the 100 mg/L COS treatment group exhibited a significant (p<0.05) inhibition of firmness reduction on the 2nd, 4th, and 6th days of storage. This suggests that COS treatment may mitigate the decrease in strawberry firmness by inhibiting the reduction in the strength of connections between strawberry cells.
The Effect of Chitosan Oligosaccharide on the Total Sugar Content in Strawberries
The sugar content in fruit is a critical indicator of its taste and quality, where higher sugar levels signify better taste and quality, leading to improved economic benefits. While some chemical treatments have been reported to positively and significantly impact the sugar content of fruit during storage, their use can lead to issues such as chemical residues.
Our data above shows that the sugar content in strawberries tends to decrease with increased storage time. However, treatment groups with 50 mg/L and 100 mg/L concentrations of Chitosan Oligosaccharide (COS) displayed a slowed reduction in total sugar content compared to the control group, with the 100 mg/L COS treatment showing significant inhibition of sugar reduction on the 4th and 6th days (p<0.05). This suggests that COS treatment can maintain the quality of strawberries during storage by slowing the decrease in total sugar content.
The Effect of Chitosan Oligosaccharide on the Titratable Acidity in Strawberries
Titratable acidity is an essential characteristic of plant quality, especially in fruits, where it, alongside sugar, is a key factor affecting fruit flavor quality. Generally, a high sugar-to-acid ratio indicates a rich flavor and superior quality in fresh produce varieties.
Therefore, quantitative research on titratable acidity holds significant importance for quality breeding in fruit trees. Studies have shown that various treatments, such as with chitosan, 1-MCP, and ethylene, can slow down the reduction of total acid content in fruit over extended storage periods. The sugar-to-acid ratio is a crucial indicator of fruit taste and quality, with a higher ratio indicating better taste.
According to data, as storage time increases, the acidity content in strawberries tends to decrease. Although there was no significant difference between the 50 mg/L and 100 mg/L COS treatment groups compared to the control, the sugar-to-acid ratio was 17.59% higher on the fourth day in the 100 mg/L COS treated group. This indicates that COS treatment can maintain the taste quality of strawberries during storage.
In Conclusion
Treatment of strawberries with chitosan oligosaccharide (COS) significantly delays the reduction in firmness that occurs during storage. Specifically, strawberries treated with 100 mg/L of COS exhibited an 11% higher firmness than the control group on the fifth day of storage. This indicates that COS treatment can significantly reduce excessive softening of strawberries, thereby extending their shelf life.
Furthermore, COS treatment has a certain delaying effect on the quality degradation of strawberries during storage. Notably, strawberries treated with a 100 mg/L COS solution four days post-harvest showed a 25.61% higher content of soluble solids, a 15.15% increase in soluble sugar content, and a 2.17% decrease in titratable acidity compared to the control group.
The results of our experiments suggest that COS can effectively regulate and control the post-harvest ripening and aging process of fruits, thereby extending their storage period. This finding underlines the potential of COS treatment as a natural and effective method for maintaining the quality and prolonging the shelf life of strawberries, highlighting its significance for both the agricultural sector and consumers seeking to preserve fruit freshness and nutritional value.