Changes in fatty acids during storage of artisanal-processed freshwater sardines (Rastrineobola argentea).

For ages, indigenous small fish species have been important in food and nutritional security of poor communities in low income countries. Freshwater fish, in particular fatty fish species are attracting a great attention because they are good sources of health promoting long chain omega-3 fatty acids. Docosahexaenoic acid (DHA, C22:6n-3), Docosapentaenoic acid (DPA, C22:5n-3) and eicosapentaenoic acid (EPA, C20:5n-3) are the main omega-3 PUFAs known to confer health benefits in humans if consumed in required amounts. While nutritionally valued, omega-3 PUFAs in fish are susceptible to oxidative damage during processing, transportation and subsequent storage. Lake Victoria sardines (Rastrineobola argentea), are rich source of chemically unstable omega-3 fatty acids DHA, DPA and EPA. Traditionally, sardines are preserved by sun drying, deep frying and smoking. Sardine products are transported, stored and marketed at ambient temperatures. Generally, uncontrolled and higher temperatures are known to increase vulnerability of polyunsaturated fatty acids to oxidation which in turn results into loss of nutritional and sensory qualities. This study investigated changes of fat acids in sun dried, deep fried and smoked sardines during storage. Lipolysis and the progressive hydroperoxides formation were monitored by free fatty acids (FFAs) and peroxide value (PV) respectively. None volatile secondary products of lipid oxidation were measured by thiobabituric acid reactive substances (TBARS). Fatty acids were analyzed by gas chromatography with a flameionization detector (GC-FID). Deep fried sardines maintained the lowest and apparently stable PV, TBARS and FFAs. Proportions of saturated fatty acids and polyunsaturated fatty acids decreased with time while that of monounsaturated fatty acids increased. Omega-3 fatty acids EPA, DPA and DHA decreased with increase in storage time. In 21 days of storage, DHA was oxidized beyond detectable levels in all sardine products. Gradual increase in FFAs in sun dried sardines was suggestive of lipid hydrolysis induced by enzymes.

Effect of clove (Syzygium aromaticum) and seaweed (Kappaphycus alvarezii) water extracts pretreatment on lipid oxidation in sun-dried sardines (Rastrineobola argentea) from Lake Victoria, Tanzania.

Small indigenous fish species play a significant role in food and nutritional security of poor communities in developing countries. Sardines (Rastrineobola argentea) are fish species of Lake Victoria known to be a good source of health-promoting omega-3 fatty acids. Open sun drying is a common and traditional sardine processing and preservation method. Sun-dried products suffer from characteristic off-flavor due to lipid oxidation which discourage product consumption and limit diversification. This study investigated the use of clove (Syzygium aromaticum) and seaweed (Kappaphycus alvarezii) water extracts as natural antioxidants to impede lipid oxidation in sun-dried sardines. Lipid oxidation was assessed by peroxide value, volatile secondary oxidation products, and fatty acid profiles. The antioxidant capacity of extracts was evaluated by total phenolic content, 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, and iron (Fe2+) chelating ability. Results showed that 5, 10, and 20 g/L clove extracts significantly reduced peroxidation in sun-dried sardines by 38.7%, 54.6%, and 56%, respectively. Clove extracts resulted in higher retention of omega-3 fatty acids and lower concentrations of secondary lipid oxidation products as opposed to seaweed counterpart. This research has demonstrated feasibility of pretreating whole, omega-3-rich small sardines with natural antioxidants to avert lipid oxidation during sun drying.

Periodic Physical Disturbance: An Alternative Method for Controlling Sitophilus zeamais (Maize Weevil) Infestation.

Sitophilus zeamais Motschulsky is the most important insect pest of stored maize in tropical regions. The objective of this study was to determine the practicality of periodic physical disturbance on S. zeamais mortality and its adoption by smallholder farmers in developing countries. In this experiment, treatments and control were arranged in a randomized block design with three replications and three storage times in three regions of Tanzania. Region was used as the blocking variable. A total of 108 clean 20-L plastic containers were each loaded with 10 kg of fresh white dent corn and 0.50 kg of maize infested with S. zeamais. For the treatment, containers were disturbed twice a day, whereas for the controls the containers were not disturbed until the end of storage. The overall mortality rate (%) after 30, 60, and 90 days of storage were 88%, 96%, and 98%, respectively. A statistically significant difference (p < 0.05) was observed for the number of live S. zeamais between the control and experimental treatments. Additionally, the number of live S. zeamais in the treatment significantly decreased as storage time increased. This study shows the potential of a feasible, simple, affordable, and effective method of protecting maize grain for small-holder farmers in developing countries without using chemicals.

A comprehensive and comparative GC-MS metabolomics study of non-volatiles in Tanzanian grown mango, pineapple, jackfruit, baobab and tamarind fruits.

Tropical fruits contribute significantly to the total fruit intake worldwide. However, their metabolomes have not yet been investigated comprehensively, as most previous studies revealed only volatile and bulk compositions. This study compares non-volatile metabolites of five fruits grown in Tanzania. A new methodology is developed for broad-spectrum GC-MS metabolomics in fruits using a new derivatization and a two dimensional peak deconvolution techniques. A total of 92 peaks were detected from fruits of which 45 were identified. Jackfruits contained the highest amount of carbohydrates, while baobab contained the highest amount of fatty acids. The highest content of organic acids was detected in tamarind. Principal component analysis revealed insights into metabolic differences and similarities, while hierarchical cluster analysis correctly grouped the fruits according to their relationships in plants' phylogenetic tree. The developed methodology could potentially be applied in large-scale studies on fruit quality, authenticity/variety, optimization of post-harvest processing and storage.

Physiochemical and antioxidant properties of roselle-mango juice blends; effects of packaging material, storage temperature and time.

A study was conducted to determine the effects of packaging materials, seasonality, storage temperature and time on physiochemical and antioxidant properties of roselle-mango juice blends. Roselle extract (20%, 40%, 60%, and 80%) was mixed with mango juice and stored in glass and plastic bottles at 4°C and 28°C. Total soluble solids, pH, titratable acidity, reducing sugar, color, vitamin C, total monomeric anthocyanins, total phenols, and antioxidant activity (FRAP) were evaluated in freshly prepared juice, and after, 2, 4, and 6 months of storage. The results showed that total soluble solids, reducing sugars, and pH increased with storage times under different storage time, irrespective of packaging materials. The acidity, color, total monomeric anthocyanin, vitamin C, total phenols, and antioxidant activity decreased during storage irrespective of storage temperature and packaging material. Loss of anthocyanins, total phenols, and vitamin C content were higher in blends stored at 28°C than 4°C.

Influence of storage temperature and time on the physicochemical and bioactive properties of roselle-fruit juice blends in plastic bottle.

Roselle-fruit juice blends were made from roselle extract and mango, papaya, and guava juices at the ratio of 80:20, 60:40, 40:60, and 20:80, % roselle: fruit juice, respectively. The blends were pasteurized at 82.5°C for 20 min and stored in 100 mL plastic bottles at 28 and 4°C for 6 months. The effects of storage time and temperature on physicochemical and bioactive properties were evaluated. Total soluble solids, pH, and reducing sugars increased significantly (P < 0.05) in some blends while titratable acidity decrease with increasing storage time. Vitamin C, total monomeric anthocyanins (TMA), total phenols (TPC), and antioxidant activity (ferric reducing ability of plasma, FRAP) in all roselle-fruit blends (40% roselle) decreased significantly (P < 0.05) at 28 and 4°C as storage progressed. Vitamin C in all roselle-fruit blends (40% roselle) decreased from 58-55% to 43-42% when stored at 28 and 4°C, respectively. TMA losses were 86-65% at 28°C and 75-53% at 4°C while TPC losses were 66-58% at 28°C and 51-22% at 4°C. Loss of antioxidant capacity (FRAP) was 18-46% at 28°C and 17-35% at 4°C. A principal component analysis (PCA) differentiated roselle-juice fruit blends into two clusters with two principle components PC1 and PC2, which explained 97 and 3% (blends stored at ambient temperature) and 96 and 4% (blends stored at refrigerated temperature) of the variation, respectively. PC1 differentiated roselle-guava juice blends which were characterized by vitamin C, TPC, FRAP, and pH, while PC2 from another cluster of roselle-mango and roselle-papaya juice blends and was characterized by TSS, RS, and color parameters (L* a* b*). However, TMA was the main variable with the highest effect on all roselle-fruit juice blends regardless of the storage time and temperature.

Effect of germination and autoclaving of sprouted finger millet and kidney beans on cyanide content.

Cyanide contents of locally purchased brown finger millet (Eleusine corocana L. Gaertner) and brown speckled kidney bean seeds (Phaseolus vulgaries var. Rose Coco) were determined using raw, germinated and autoclaved samples. The aim was to establish the extent of cyanide content increase resulting from the germination process and the effectiveness of the autoclaving process on the reduction of cyanide levels in the samples, for safety considerations. Autoclaving was carried out at 121degree C for 20 minutes. It was found that germination increased the cyanide content by 2.11 to 2.14 fold in finger millet for laboratory processed samples. In the case of kidney beans the increment was 1.76 to 1.77 fold for laboratory samples. The increments for field processed samples were in the same range as those for laboratory samples. Autoclaving reduced the cyanide content to between 61.8 and 65.9 % of the original raw contents for finger millet and between 56.6 to 57.8% in the case of kidney beans. The corresponding reductions for field samples were also found to be within the same ranges as the laboratory processed samples. It was concluded that autoclaving significantly reduced the cyanide levels in germinated finger millet and kidney beans.

Quality evaluation of honey harvested from selected areas in Tanzania with special emphasis on hydroxymethyl furfural (HMF) levels.

The physicochemical properties of honey harvested from popular honey-producing areas in Tanzania were investigated. Honey from Shibe-Dodoma had the highest values of specific gravity, total acidity, free fatty acid content, diastatic number, overall acceptability, and lowest hydroxymethyl-furfural (HMF) level as compared to honey samples from other areas. There was no significant difference (p > 0.05) in terms of HMF in the other honey samples from Tanga, Morogoro, Same, Arusha, and Tabora. HMF levels in all honey samples were far below the maximum acceptable level of 40 mg/kg as recommended by the Codex Alimentarius Commission Standards before storage for 6 months. No traces of streptomycin and phenol were detected in all honey samples. It was concluded that according to the values of the studied quality parameters, the types of Tanzanian honey obtained from the popular honey producing areas may be judged to be of high quality.