Vitamin C stability in pineapple, guava and baobab juices under different storage conditions using different levels of sodium benzoate and metabisulphite

Vitamin C is one of the most important vitamins in fruit based products and its stability is very critical to guarantee its availability. Stability of vitamin C in baobab, guava and pineapple juices stored at room (22.4°C ± 1.3), chilling (-1.2°C ± 0.1) and freezing (-17.3°C ± 0.2) temperatures and using 0.05% sodium benzoate, 0.005% sodium metabisulphite and combined use of sodium benzoate and metabisulphite at 0.04 and 0.005% respectively was investigated. Results from the study revealed that both storage conditions and levels of the preservatives used significantly affected vitamin C stability in all the three types of juices used. Vitamin C contents were 74.4, 52.4 and 34.7 mg/100 mL for baobab, guava and pineapple juices on the first day of processing. Furthermore, vitamin C was found to be more stable in freezing storage conditions and the combined use of sodium benzoate and sodium metabisulphite at 0.04 and 0.005%, respectively was more effective in stabilizing vitamin C in the fruit juices than the other preservative levels used. It can be concluded that vitamin C stability in the three types of juices was influenced by storage temperature conditions, storage time and levels and types of preservatives used.Keywords: Stability, baobab, guava, pineapple, vitamin C, sodium benzoateAfrican Journal of Biotechnology Vol. 12(2), pp. 186-19

Phytochemical composition of four selected vegetable spices commonly consumed in Malawi

Spices, regardless of source, play an important role in enhancing or improving flavor of foods or dishes. In this study, determination of phytochemical composition with respect to total phenolic compounds, antioxidant capacity and vitamin C was conducted in four selected vegetable spices consumed in Malawi, namely Allium cepa L, Allium sativum L, green bell pepper (Capsicum annum L.) and Zingiber officinale. Results showed that total phenolic composition, in mg GAE/100 g, was highest in Zingiber officinale rhizomes (326.5±0.39) followed by Allium cepa L. (169.7±0.00), green bell pepper (124.9±0.20) and Allium sativum L. (72.72±0.39), respectively. Results further showed that Zingiber officinale had the highest antioxidant capacity and reducing power and the lowest vitamin C content, in the range of 21.78±0.21 mg AAE/100 g, 24.35±2.24 mg AAE/g and 3.61±0.23 mg AAE/100 g, respectively compared to the other vegetable spices. On the other hand, vitamin C content was highest in Allium sativum L followed by red Allium cepa L registering values of 455.0±2.12 and 443.4±2.50 mg AAE/100 g, respectively. The reducing power (in mg AAE/g) of the vegetable spices was highest in green bell pepper (Capsicum annum L.) with the value of 17.11±1.549 followed by red Allium cepa L. (9.519±0.860) and Allium sativum L. (5.922±0.778), respectively. Total tannins content, in mg TAE/g, was highest in Allium sativum L, which registered the value of 159.56±4.84 followed by Zingiber officinale (91.53±0.33), bell  pepper (79.94±0.21) and Allium cepa L (49.36±1.98). Furthermore, phytic acid and oxalic acid contents were highest in Zingiber officinale registering values of 5.504±0.822 mg/kg and 37.25±2.83 mg/g, respectively. Red Allium cepa L. was found to contain 20.53±0.916 mg/g oxalic acid but had the lowest phytic acid content registering the value of 2.057±0.095 mg/kg. It can be concluded that the high phytochemical composition in the four vegetable spices, with low antinutrients like phytic and oxalic acids, can play an important role in improving human nutrition and health of consumers.&nbsp

Determination and comparison of vitamin C, calcium and potassium in four selected conventionally and organically grown fruits and vegetables

It is evident that the growing interest in organically grown produce has correspondingly necessitated the debate on the nutritional supremacy between organically and conventionally grown produce. A study was carried out to determine and compare vitamin C, calcium and potassium in organically and conventionally grown cabbage, carrots, Cos lettuce and Valencia oranges. Samples were purchased from local supermarkets within Central Coast, New South Wales in Australia from late March to early April 2007. Vitamin C content was determined by 2,6-dichloroindophenol titrimetric method while calcium and potassium were determined by atomic absorption spectroscopy. Results from the study showed inconsistent pattern with respect to vitamin C, calcium and potassium contents in the conventionally and organically grown samples. No significant differences were observed in vitamin Ccontent in conventionally and organically grown cabbage, carrots and Cos lettuce while significant differences were observed in Valencia oranges which showed higher vitamin C content in organicValencia oranges as compared to conventional ones (51.8 to 43.4 mg/100 g fresh weight). Results on calcium and potassium contents showed significant differences in all the samples with the trend ofhigher values for organically grown cabbage, carrots and Cos lettuce as opposed to their conventionally grown counterparts. However, for Valencia oranges, results showed that the calcium and potassium contents were significantly higher in conventional Valencia oranges compared to the organic Valencia orange (54.5 and192.0 mg to 51.8 and 189.5 mg/100 g, respectively)