Titrable Acidity. The acidity increased after 30 days from initial acidity adjusted to 0.5% during preparation in all jams. In any of the jams, overall titrable acidity significantly reduced during storage period (30–60 days), from an overall average of 0.898% to 0.806% (Table 2). The interactive effects decreased the acidity significantly after 60 days of storage as in Pineapple-orange and Pineapple-orange-banana jams (Table 4). Although increase in the acidity in other jams was observed, it did not increase significantly as a result of the interactive effect after storage. Increase in acidity of fruit jams was reported earlier to be a result of ascorbic acid degradation or hydrolysis of pectin (Cruess 1958; Sogi and Singh 2001). A maximum of 1.6% acidity and a minimum of 0.64% acidity were observed in pineapple-orange jam and pineapple jam, at 30 days and 60 days storage, respectively.
Reducing Sugars. The reducing sugars in all jams increased after 60 days of storage, except for pineapple-banana jam and orange-banana jam as a result of interaction between fruit pulp(s) and period of jam stored (Table 4). A maximum of 16.50% reducing sugars were present in pineapple-orange-banana-papaya jam and in pineapple-orange-banana jam at 60 days, and a minimum of 6.5% reducing sugars was noted in pineapple jam (Table 4) after a 30-day storage period, respectively.
Total Sugars (Invert). Total sugar (invert) contents among the jams differed significantly; storage period did not affect its contents (Tables 2 and 3) in the jams. The interactive effect between pulp combinations and storage periods significantly changed the total sugars (invert) (Table 4). It ranged from 31.7 to 57.9% at 30 days and from 33.3 to 51.2% at 60 days of storage for the different jams (Table 4).