Changes in potato after different thermal processes

Undesirable thermal processes or storage conditions lead to physical and chemical quality loss of every food. The objective of this study was to determine the total solid content, starch, reducing sugars, nitrates and nitrites in raw and thermal processed red and white potato samples purchased from different geographic origin in Croatia. The potatoes were processed with and without the skin, and cooking processes were carried out in classic way, in the pressure cooker and in the microwave oven. Standard methods of analysis for above-mentioned parameters were used. The results showed no significant influence (P < 0.05) of the geographic origin on investigated parameters in raw samples (except for nitrates), but there were significant differences (P < 0.05) in composition between the kinds of samples (red and white). Thus, samples of white potato had higher total solids, starch and reducing sugars content than red potato samples, while red potatoes had higher nitrites and nitrates content. Thermal treatment showed that the total solid content is higher in potatoes processed with skin then those processed without the skin. The starch content in both kinds of potatoes increased after thermal processes if potato was processed without skin. The content of reducing sugars was the highest in samples of raw potato. The nitrites and nitrates content were decreasing during thermal treatments. Thermal processing (classic way, under pressure or with microwaves) and the manner on which the potatoes were cooked (with or without skin) significantly influenced on all investigated parameters especially in red potatoes samples.