Asanda Mditshwa

Phytochemical content, antioxidant capacity and physicochemical properties of pomegranate grown in different microclimates in South Africa

We investigated the antioxidant and physicochemical properties of pomegranate (Punica granatum cv. Bhagwa) fruit grown in three microclimates in South Africa. The physicochemical properties of fruit peel and arils differed among the growing locations, including weight and redness color of both peel and arils. Contents of vitamin C, anthocyanin and total phenolics were 0.67–1.41 mg ml−1, 0.07–0.16 mg ml−1 and 8.54–13.91 mg ml−1, respectively. Fruit grown in locations with high light intensity had higher vitamin C content and lower phenolic content than those of fruit from low-altitude locations and high light intensity. The pH of juice did not significantly differ among locations, whereas significant variation was observed in total soluble solids (TSS), titratible acidity (TA) and TSS:TA ratio. Fruit from locations with low rainfall had high TSS and low TA. Principal component analysis was used successfully to classify fruit by growing location on the basis of antioxidant and phytochemical contents.

Classification of 'Granny Smith' apples with different levels of superficial scald severity based on targeted metabolites and discriminant analysis

To study the metabolic changes in ‘Granny Smith’ apples with different severities of superficial scald, fruit were stored in normal refrigerated air (0°C, 95% RH) for 12 weeks followed by 7 d shelf-life under room conditions (20°C, 65% RH). Fruit were graded to five groups based on scald severity and analysed for ethylene, α-farnesene and 6-methyl-5-hepten-2-one (MHO) levels. Reactive oxygen species (ROS) were measured by confocal laser-scanning microscopy on apple peel treated with fluorescent probe 2’,7’-dichlorodihydrofluorescein diacetate. Ethylene production rate, α-farnesene and MHO contents and ROS intensity increased with increasing scald severity but declined in severely scalded fruit. Malondialdehyde (MDA) concentration in fruit peel, a measure of membrane damage, increased linearly (R=0.891) with increase in scald severity. Discriminant analysis was used to classify fruit by scald severity on the basis of metabolites accumulated. The stepwise model indicated that three attributes (ROS, ethylene production and MDA) contributed significantly (R 2 ≥0.5) to the separation of the five scald severity indexes, with ROS having the highest contribution (partial R² =0.961; p<0.0001), followed by ethylene (R 2 =0.718; p<0.0001) and MDA (R 2 =0.578; p<0.0001).

Effect of ultraviolet irradiation on postharvest quality and composition of tomatoes: a review

Ultraviolet (UV) irradiation has recently emerged as a possible alternative to currently used postharvest phytosanitary treatments. Research has also highlighted other benefits associated with UV irradiation in postharvest technology. This review presents the effects of UV irradiation on postharvest and nutritional quality of tomatoes. The application of UV irradiation on tomatoes is discussed including its effect on biological (respiration rate, ethylene production and microbial growth), physico-chemical (firmness, colour, total soluble solids and titratable acidity) and nutritional (vitamins, carotenoids, phenolic and antioxidants) quality. UV-treated tomatoes have shown resistance to microbial growth and decay. Although UV irradiation reduces the loss of vitamin C during storage, the loss of vitamin E remains a concern. UV treatments lead to higher antioxidant capacity, flavonoids and phenolic content. UV irradiation significantly reduced carotenoids in certain cultivars. Based on the literature reviewed, the success of UV irradiation treatments is cultivar-dependent. While improved retention of phytochemicals has been reported in UV-C treated fruit, increased losses have been reported in certain cultivars. Research efforts on the development of cultivar-specific UV irradiation protocols are warranted. The effect of harvest maturity and seasonal differences in the efficacy of UV treatments is required to be investigated.

Antioxidant content and phytochemical properties of apple ‘Granny Smith’ at different harvest times

Understanding the biochemical composition of fruit to be stored could be used as a tool for planning postharvest management to maintain quality and reduce losses of fresh fruit. This study evaluated the effects of harvesting fruit seven days before (H1) and at optimal commercial harvest (H2) on the antioxidant contents and phytochemical properties of ‘Granny Smith’ apples. Both ascorbic acid content (345.6 vs 227.0 mg g−1) and total antioxidant capacity (100.82 vs 82.37 μM g−1) were significantly higher in H2 fruit, whereas concentration of total phenolics was slightly higher in fruit harvested at H1 (25.34 vs 30.87 mg g−1). Phenolic compounds including catechin, epicatechin and quercetin were significantly higher in fruit harvested at H1 compared with H2. These results showed that differences in antioxidant capacity and concentration of phytochemical compounds are the major factors segregating fruit harvested before and at optimal commercial harvest.