A study of some important vitamins and antioxidants in a blackcurrant jam with low sugar content and without additives.

Blackcurrant (Ribes nigrum) jam was manufactured with the aim of producing a jam with a low sugar content, and without any additives. Four temperatures were investigated, namely 60 degrees C, 76 degrees C, 92 degrees C and 97 degrees C. Processing time varied between 1-20 min. After processing, the highest content of ascorbic acid was found in the jam processed at 97 degrees C for 1 min, which contained 63.3 +/- 2.6 mg ascorbic acid/100 g jam. At all combinations investigated more than 60% of the original amount of ascorbic acid was retained after manufacturing and packaging. The jam made at 92 degrees C was stored in a shelf-life study for 13 months. The jam was then stored at 8 degrees C, ambient temperature and at 37 degrees C. At ambient temperature the jam was stored both in dark and in daylight, at 8 degrees C and at 37 degrees C the jam was stored in dark. After 13 months of storage, at 8 degrees C, 60% of the amount of ascorbic acid and 29% of the amount of anthocyanins were retained. In the jam stored at higher temperatures less of both was retained. The beta-carotene in the jam was found to be stable throughout the whole shelf-life study. Exposure to light did not have any effect on any of the components studied. The degradation of anthocyanins was best described by a second-order reaction and the activation energy was determined to be 90 kJ/mol. A jam of blackcurrant may be considered as a good source of vitamins and antioxidants after one year, if certain precautions concerning manufacture and storage conditions are taken.

Digestibility of processed food protein.

An overview is given on the effects of food processing on the protein digestibility. Beneficial effects of food processing are primarily observed in a range of plant foods containing toxic substances and/or anti-nutrients (legumes, cereals, some seed food). Digestibilities improve by heating, soaking, germination and fermentation. These processing steps reduce the amount of active enzyme inhibitors through extraction, inactivation by heat or microorganisms, or by compositional modification through germination. Reduced protein digestibility is primarily associated with excessive heat, exemplified by the comparatively low digestibility of ready-to-eat breakfast cereals. Experiments with model systems indicate that some caution should be observed with the use of alkalis in food processing, and with products prone to the Maillard reaction.