Processing of marula (Sclerocarya birrea subsp. Caffra) fruits : a case study on health-promoting compounds in marula pulp

Marula is a multipurpose tree from Southern Africa, used by local people for its fruit, and cosmetic oil from the seed and for medicinal products from the bark and leaves. Fruits are eaten raw, or used to prepare juices, jams, conserves, dry fruit rolls, or fermented to make alcoholic beverages like beer, wine and Amarula. The fruit is a vital source of vitamin C for rural people most of whom cannot afford other more expensive sources of vitamin C. The specific processing methods and conditions of making marula juice vary among different regions. This thesis investigated the fate of antioxidants, i.e. vitamin C, and their activities due to heat processing and fermentation of the marula pulps and its juices. The results showed that marula fruit pulp has a vitamin C content higher than that of most fruits, ranging from 62 mg/100 g fresh weight– to over 400 mg/100 g. Juice production was optimized by an experimental design combined with response surface modelling: adding pectinase (in the range of 0.1 to 0.14%) increased the yield of marula juice by 23%. The optimal extraction temperature for the content of vitamin C and polyphenols as well as for the antioxidant activity ranged between 40 and 60°C. At heating temperatures below 125ºC, ascorbic acid in marula pulp was about 15-fold more stable than in mango and guava pulp. The results further revealed that marula peel contained more volatile compounds (75) including all the identified volatiles (41) of the flesh. Marula fruit is a rich source of vitamin C and other antioxidants. The use of unfermented juice should be encouraged since it can contribute to the energy intake of the marula juice drinkers. Marula juice is a rich source of natural antioxidants. In addition, marula processors are advised to incorporate (part of) the skin in products such as juices, jams, jellies and alcoholic beverages during processing to enhance the unique characteristic marula flavor in the products which are currently claimed not to have a strong marula like flavour.</p

The effect of temperature and time on the quality of natural fermented marula (Sclerocarya birrea subsp. Caffra) juice

This paper presents the effects of fermentation on the retention of vitamin C, total polyphenols and antioxidant activity in the naturally fermented marula juice. The fermentation conditions have been varied: temperature ranged between 20 and 40 °C and fermentation time from 1 to 8 days. Marula juice fermented at higher temperatures ranged between 30 and 40 °C for 6 to 4 days retained high antioxidant activities, and they were positively correlated to its ascorbic acid and phenolic content. The values obtained ranged between 0.0239 ± 0.0051 and 0.029 ± 0.0038 µmol/mg for Trolox Equivalence Antioxidant Capacity, 870 ± 80 and 960 ± 130 mg/100 ml for total phenolic content and 90 ± 6 and 159 ± 15 mg/100 ml for ascorbic acid. Overall, fermented marula juice can be used as a good source for natural antioxidants

A review of the proximate composition and nutritional value of Marula (Sclerocarya birrea subsp. caffra)

This review critically evaluated literature on proximate composition and nutritional value of Marula in comparison with other tropical and indigenous fruits in order to identify areas for future research. It was found that nutrients content and processing methods of Marula fruit varied greatly from study to study and according to place of origin, soil, climate, handling, analytical methods used and time that lapsed after harvesting before analysis took place. Marula fruit pulp is reported to have vitamin C content higher than that of most fruits, ranging from 62 mg/100 g to over 400 mg/100 g. Additionally, Marula fruit is reported to have an antioxidant capacity of between 8 and 25 mM, (ascorbic acid equivalents) and a total phenolic content ranging from 7.5 to 24 mg/g dry weight gallic acid equivalent. Marula kernels are also a good source of protein, oil, magnesium, phosphorus and potassium and their oil is used in food preparations. Marula fruits could play a vital role in terms of nutrition to rural community who rely on the usage of the fruits, as they do not have easy access to other sources of nutrients. Recommendation given for future research includes improving Marula fruits juice extraction and yields, investigating the effect of processing and storage on the retention of nutrients such as vitamin C and its antioxidant capacity in processed and unprocessed Marula products and further identifying Marula fruits flavor compounds and their effect on processing and storage

Kinetics of thermal degradation of Vitamin C in Marula Fruit (Sclerocarya birrea subsp. caffra) as compared to other selected tropical fruits

The kinetics of the thermaldegradation of vitaminC of marula, mango and guava pulp at different heat treatments at temperature ranging from 80 to 150 °C were investigated. For temperatures lower than 125 °C, the ascorbic acid in marula pulp was about 15 fold more stable to heat than the ascorbic acid in mango and guava pulp. The results showed that a simple first order degradation model could not describe the vitaminCdegradation as biphasic behaviour was observed. Therefore the model was transformed in a two-fraction model in which the vitaminC content is divided in relatively stable and instable fractions. Marula had a low kd1,100°C of 7.2 × 10-3 min-1compared to kd1,100°C of 1.2 × 10-1 min-1 for guava and 1.3 × 10-1 min-1 for mango. Guava had the highest activation energy, Ea of 58 kJ/mol, followed by mango with 39 kJ/mol and then marula with 29 kJ/mol

Kinetics of thermal degradation of Vitamin C in Marula Fruit (Sclerocarya birrea subsp. caffra) as compared to other selected tropical fruits

The kinetics of the thermaldegradation of vitaminC of marula, mango and guava pulp at different heat treatments at temperature ranging from 80 to 150 °C were investigated. For temperatures lower than 125 °C, the ascorbic acid in marula pulp was about 15 fold more stable to heat than the ascorbic acid in mango and guava pulp. The results showed that a simple first order degradation model could not describe the vitaminCdegradation as biphasic behaviour was observed. Therefore the model was transformed in a two-fraction model in which the vitaminC content is divided in relatively stable and instable fractions. Marula had a low kd1,100°C of 7.2 × 10-3 min-1compared to kd1,100°C of 1.2 × 10-1 min-1 for guava and 1.3 × 10-1 min-1 for mango. Guava had the highest activation energy, Ea of 58 kJ/mol, followed by mango with 39 kJ/mol and then marula with 29 kJ/mol