Effect of light conditions on physico-chemical properties of pineapple juice with addition of small pineapple pieces during storage

Antioxidant status, ascorbic acid concentration, 5-hydroxymethyl-2-furaldehyde (HMF) formation and total colour changes in a pineapple juice with the addition of small pieces of pineapple stored up to 26 weeks at 7 C at different light conditions (darkness, day light) were characterized. Ascorbic acid losses reached after 26 weeks approximately 23% (day light) and 37% (darkness) of the original concentration. These trends were confirmed also by comparison of kinetic constant values. The impact of light and time on HMF formation was negligible, when maximum concentration of HMF at a level of 2 mg.l(-1) was found. Slight decrease of total polyphenolic compounds concentration without respect on storing conditions was noticed, with minimum after 8 weeks of storage. Decomposition of sample components and the formation of low-molecular weight phenolic fractions are supposed. Gradual decrease of antioxidant capacity of the juice was also noticed, more apparent for the samples stored at day light with fluctuations caused by samples hetero-genity and metal ions content. Juice yellowness was most significantly influenced by the processing and storage under given conditions, change of which was the most intensive during 4th week of the storage. Long-term storage for up to 26 weeks resulted in a significantly increased yellowness for both storage variants.