Abstract
This work was aimed at investigating the effect of storage temperature on the physicochemical, nutritional, and microbial quality of soursop juice. Physicochemical quality was determined by measuring changes in pH, titratable acidity, total soluble solids and colour (L*a*b* values). Ascorbic acid levels, total phenolic content and total antioxidant capacity were analysed to determine the effect of storage temperature on nutritional quality. The changes in aerobic mesophilic and psychrophilic bacteria, lactic acid bacteria, Enterobacteriaceae, as well as yeast and moulds were enumerated to determine the effect of storage temperature on microbial quality. Soursop juice was pasteurised at 85°C for 5 min and stored at varying temperatures of 4, 10 and 25°C. Storage was carried out for 12 weeks at both 4 and 10°C, while at 25°C the juice was stored for 3.5 weeks when visible signs of spoilage was detected. Storing soursop juice at 4oC did not affect quality, however, at 25°C, decreases in pH and total soluble solids with an increase in titratable acidity was observed. In addition, a faster rate of ascorbic acid degradation was observed at 25°C. The main group of microorganisms that were responsible for the spoilage of soursop juice stored at 25°C were lactic acid bacteria, and yeasts and moulds. The results of this work show that pasteurised soursop juice can be stored at refrigeration temperatures without changes in quality. Key words: Soursop juice, pasteurization, storage temperature, lactic acid bacteria, ascorbic acid.
Highlights
Extraction of juice from fruits can be used to improve the usage of fruits as the extracted juice can be transported and stored (Bhardwaj and Pandey, 2011)
Pasteurization resulted in reductions in ascorbic acid levels, total phenolic content and total antioxidant capacity; Effect of storage temperature on the microbial of soursop juice
Yeast and moulds were the predominant group of microorganisms that were able to grow in the soursop juice
Summary
Extraction of juice from fruits can be used to improve the usage of fruits as the extracted juice can be transported and stored (Bhardwaj and Pandey, 2011). The extraction process, can lead to microbial contamination, which can limit the shelf life of the extracted juice. To improve the shelf life of the extracted juice, thermal processing methods such as pasteurization can be carried out to reduce the level of microbial contamination and other reactions (enzymatic and nonenzymatic) which can lead to spoilage (Rivas et al, 2006). 2016; Umme et al, 2001; Wibowo et al, 2015) Some of these changes may affect colour and flavor which in the end may reduce the sensory acceptability of the juice (Umme et al, 2001). The temperature of storage usually influences the changes that occur during storage It is, important to investigate the effect of storage temperature on the changes in fruit juice after pasteurization
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