Analysis of anthocyanins content and microbiological quality control in fresh and frozen raspberry fruit

Raspberry (Rubus idaeus L.) is a plant from the rose family and the most important berry-type fruit in our country. The most significant sorts of raspberries grown in Serbia are the red sorts, namely Willamette, Meeker, Gradina, Malling exploit and Skina. Raspberry fruit may be used either fresh or as a raw material in food industry, for the production of fruit juice, nectar, syrup, concentrate, dried and frozen fruit. The goal of this paper is to determine pH, titratable acidity (as citric acid), soluble solids, concentration of anthocyanins, vitamin C and total polyphenols, and to perform sensory analysis and microbiological quality control in both fresh and frozen fruit. pH value was measured with pH-meter. The concentration of acids was determined by the volumetric method, by titration with NaOH. The dry matter was measured by a refractometer. The concentration of anthocyanins was determined by the spectrophotometry method. The concentration of vitamin C was determined using the volumetric method. The concentration of polyphenol compounds was determined according to the Singleton method. The microbiological methods of detection and counting microorganisms were performed according to ISO standards. The results of this study have shown that both fresh and frozen raspberries are a good source of anthocyanins, indicating that their consumption is favorable for human health and that they may be useful in the production of functional food. The microbiological analyses have shown the absence of L. monocytogenes and Salmonella spp., while the concentration of Enterobacteriaceae and E. coli was below 10 cfu/g in both fresh and frozen raspberry fruit.