This study reports the effectiveness of various concentrations of ascorbic acid, citric acid and oxalic acid used as acidulants to regulate activities of antioxidant, polygalacturonase, pectin methylesterase and polyphenol oxidase of fresh-cut wax apple (Syzygium samarangense). The samples of fresh-cut wax apple, cut in wedges (1/8), were dipped into ascorbic acid, citric acid and oxalic acid at four different concentrations (0, 0.5, 1.0, 1.5 and 2.0%) for 1 min. The changes in the parameters were monitored for nine days while they are in storage at 4�C. Fruit treated with oxalic acid contained the highest antioxidant activity, followed by those treated with citric acid and ascorbic acid. The activity of antioxidant increased with the increasing storage period. Similar effects of acid treatments were detected for total phenolic contents. There was no effect of types of organic acids on polygalacturonase activity but acid dipping reduced the activity of the enzyme. In contrast, types of acids and acid concentration did not alter the activity of pectin methylesterase activity. Activity of pectin methylesterase in fruit sampled on day 6 and 9 were higher than those of the earlier dates. Similar pattern of effects of acid treatment were observed for polyphenol oxidase activity. � 2015 Asian Network for Scientific Information.

Brown rot caused by Monilinia fmcticola is one of most serious postharvest diseases infecting red-flesh dragon fruits. Once infected, the quality of fruits is drastically reduced and the fruits are unlikely to be acceptable within a few days after infection. With the possible mechanism of Ca in controlling the growth of the fungus by reducing the activity of pectolytic enzymes of the causing organism and strengthening the host cell wall, the fruits were treated with four concentration of CaCl2 (0, 1.0, 2.0, 3.0 and 4.0 g L-1) at postharvest stage for 30 min, then inoculated with spore suspensions of M. fmcticola (106 spores ml-1). Results showed that the severity of brown rot was reduced with increasing CaCl2 concentration and this was supported by a strong negative correlation between fruit peel, Ca and disease severity (r=-95). Overall, the beneficial effects of elevated CaCl2 on quality parameters i.e., soluble solids, acidity and firmness were more apparent on severely infected fruits.

Response surface methodology (RSM) was employed for optimising the formulation and processing parameters of red cabbage-roselle mixed drink. In this study, four independent variables namely red cabbage-roselle extracts concentration (30 to 70%), stingless honey concentration (1–10%), pasteurisation temperature (70–90°C), and pasteurisation time (30–300 s) were studied in order to determine the effect of the formulation (ingredients) and processing parameters towards the colour and anthocyanins content of the mixed drinks. Thirty different experimental combinations generated by RSM design were studied on the responses i.e. colour values (L*, a*, b*) and total anthocyanin content of red cabbage-roselle mixed drink. The optimal formulation and processing condition were obtained with a 70% combination of red cabbage-roselle extracts concentration and 1% of stingless honey concentration, with pasteurisation temperature, and time of 70.01°C and 284.07 s, respectively. In order to verify the models, the experimental values were compared with the predicted values to check the adequacy of the models. The experimental values were found to be in agreement with those predicted, thus, indicating the suitability of the models used by RSM to optimise the formulation and processing parameters of mixed drinks made from red cabbage and roselle extracts. © 2020, Malaysian Society of Applied Biology. All rights reserved.

Fruits harvested at different maturity possess different biochemical constituents and physiological properties that make the fruits may react somewhat differently to the postharvest treatment. A study to examine the activity of Polygalacturonase (PG) and Pectin Methylesterase (PME) enzymes during storage in dragon fruit (Hylocereus polyrhizus) harvested at 28 days (Index 3) and 34 days (Index 5) after anthesis and postharvest treated with 0, 2.5, 5.0 and 7.5 g L-1 CaCl2 was performed. The PG activity was lower in younger fruit and vice-versa for PME activity. Increasing concentration of CaCl2 effectively reduced the activity of both enzymes. PG activity for fruit treated with 0, 5 and 7.5 g L-1 CaCl2 increased linearly with the time of storage while its activity for the fruit treated with 2.5 g L-1 CaCl2 was lower at the beginning of storage. PG activity of Index 5 fruits increased almost linearly during storage while its activity in Index 3 fruits was low at the early days of storage and later continued to increase until day seven. At both maturity indices, the PME activity was low at the early days of storage and later continued to increase until day seven. Overall, results obtained indicated that CaCl2 postharvest treatment reduced both PME and PG activities thus slowing down the softening process giving an evident that calcium possess a distinguishable role in the reducing softening of fruit, regardless of maturity index. � 2013 Science Publication.