Investigating the effect of different physical and chemical parameters on the quality and stability of blackberry-enriched anthocyanin pigments

Abstract
Introduction: Anthocyanins are the most important flavonoid pigments which have health benefits for concumers due to their high antioxidant activity. These compounds are non-toxic and water-soluble, and with attractive and bright colors of red, blue, and purple, are good alternatives to harmful chemical dyes. Blackberry fruit is one of the rich sources of anthocyanins in nature. Blackberry anthocyanins have been considered as healthy and effective food colors in the food industry due to the presence of dark purple color along with abundant nutrients. However, unfavorable physical and chemical conditions may cause spoilage and color changes in the natural pigments of this fruit.
Blackberry fruit is a good source of vitamins A, B, C, E and K as well as iron, potassium, manganese, magnesium, niacin, riboflavin, folic acid, glucose and tannin. The presence of many nutrients along with high antioxidant activity has made this fruit to be considered as a suitable source for meeting the daily need for various micronutrients. Based on this, with the correct processing of blackberry extract, its anthocyanins can be used not only as a natural color but also as a harmless sweetener and a substance with excellent micronutrient properties in various food industries.

Objectives: the purpose of this study is a comprehensive study on the degradation factors of blackberry anthocyanins to find appropriate protection methods, and their subsequent use in the food industry.

Material and Methods: In this research, various methods of extracting color from blackberry fruit were investigated, including the use of different solvents and different temperatures, and finally it was determined to use acidic ethanol and acidic methanol solvents and then evaporate the solvent in a vacuum and low temperature. It has the best efficiency in extracting color from blackberry fruit. These results show that the more the structure of the solvent is similar to the structure of the extracted pigment, the higher the percentage of extraction. Considering less toxicity, 0.1% acidic ethanol solution (ethanol + hydrochloric acid) was considered as the extraction solvent. In summary, liquid-solid phase extraction method, extractive phase separation and subsequent evaporation of the extraction solvent in vacuum and low temperatures of 30 to 40°C were used to extract anthocyanin. After extracting and enriching the anthocyanins of blackberry fruit and determining its properties, the effect of various physical and chemical parameters such as temperature, light, presence of enzymes, different pHs, presence of oxygen, and the addition of authorized food additives on the quality and stability of this pigment was investigated and ways of optimization them were evaluated.
Results and Discussion: By performing various tests, it was found that the use of acidic ethanol solution provides the highest color extraction efficiency with the lowest amount of degradation. Examining the physical and chemical properties of the extracted anthocyanin showed the presence of 15% dry matter, 85% moisture and 14.5% soluble solids. Also, the extracted color has acidic properties. Based on the obtained HPLC chromatogram analysis, five anthocyanins were identified in the blackberry extract, and cyanidin 3-glycoside was the dominant type of blackberry color anthocyanin. The amount of absorption and total anthocyanin in the enriched extract of blackberry fruit was found to be 0.32 and 24.3 mg/liter, respectively, which is a significant amount and indicates the appropriate enrichment of the extracted anthocyanin. It was also found that by using the wind tunnel it is possible to dry and powder the paint without reducing the quality. Investigating the stability of enriched anthocyanin pigments showed that light and temperature are two important factors in the stability of blackberry anthocyanins, and by removing light and reducing temperature, the stability of anthocyanins can be increased to a great extent. . The natural enzymes present in the blackberry fruit destroy the chemical structure of cyanidins, and by deactivating them, the color of the product is well preserved. Also, the enzyme helps to prevent the growth of molds. The highest concentration of anthocyanin and the highest color intensity were obtained in the range of pH = 3-4, which corresponds to the natural pH of the extracted solution (pH = 3.2) and the further away from the natural pH of the product, the concentration anthocyanin decreases. However, anthocyanin is more stable under acidic conditions and has a higher concentration. Oxygen also destroys anthocyanins. However, the use of nitrogen gas not only prevents the destruction of pigment by oxygen, but also prevents the growth of mold. By adding food additives such as sorbitol, glucose, carbon dioxide and citric acid, the color stability of the extracts increases and citric acid prevents the growth of molds. Finally, according to the quality and intensity of the enriched anthocyanin color obtained in this research, it is possible to use it in the food industry.
Conclusion: The results demonstrated that cyanidin-3-glycoside is the main anthocyanin in blackberry fruit. Light, temperature, changing pH, and the presence of oxygen reduce the stability of anthocyanins by 56.5 to 88.2%. On the other hand, the addition of authorized food additives such as carbon dioxide, citric acid, glucose, sorbitol, and nitrogen gas helped stabilize the pigments. Thus, the samples retained their color up to 98.8, and 93.6%. in darkness, and indirect light, respectively.
Keywords: Anthocyanin, Blackberry, Stability factors, Natural pigments