Evaluation of cultivar susceptibility and storage periods towards aflatoxin B1 contamination on pistachio nuts
Aflatoxins (AFs) are potent sources of health risks to both humans and animals. Among them, AFB1 is the most hazardously toxic and the most frequent in various food commodities, including pistachio nuts. In this survey, the effect of the storage period on AFB1 accumulation on pistachio nuts was investigated. A total of 49 samples collected during the crop year of 2005 from the most cultivated pistachio cultivars in Tunisia were rapidly screened by enzyme-linked immunosorbent assay (ELISA) combined with an immunoaffinity step. The obtained results showed that the contamination of pistachio nuts has occurred clearly after two years of storage for all the tested cultivars except the case of Mateur variety and Thyna ecotypes. In this study, the cultivar Mateur was found to be the most susceptible cultivar to contamination by AFB1. After 4 years of storage, the average contamination levels in nut samples ranged from 2.7 ± 0.3 to 12.7 ± 2.2 µg/kg for AFB1, according to the cultivar. These levels exceeded the maximum permitted limit of 2 µg/kg set by the European Commission in nuts.
Lipid characterization of local pistachio germoplasm in central and southern Tunisia
Pistachio germoplasm cultivated in traditional areas of Tunisia presented an interesting genetic diversity. The study was conducted to assess desirable biochemical characteristics from the rich local germoplasm in pistachio ecotypes. Kernel samples of the widely cultivated Mateur cultivar and 89 ecotypes from Sfax and El Guetar localities were collected during 2 years. Oil content and fatty acid composition were assessed. Fat content and fatty acid composition differed significantly among local ecotypes. The mean fat content of pistachio ecotypes ranged from 56 to 78%. Palmitic acid content varied between 7.1 and 12.9%. In addition, stearic acid was found as a minor saturated fatty acid in pistachio kernels; levels varied from 0.7 to 2.8%. Oleic acid content ranged from 56.1 to 80.7% with a significant difference over the different ecotypes. Linoleic acid varied between 8.2 and 29.7%. Mateur cultivar showed slight variations of fat content and fatty acid composition in the localities investigated. Certain ecotypes, such as Loby7 (fat content 78.5%), Sridique1 (80% Oleic, 9% linoleic), Ibala3 (76.8% oleic, 9.5% linoleic) from Sfax, and EPE2 (80% oleic, 8.2% linoleic), BMS3 (79.4% oleic, 9% linoleic), HAB3 (78.6% oleic, 9.9% linoleic), AMMS4 (78% oleic, 11.2% linoleic), and ABT2 (76.8% oleic, 12.1 linoleic) from El Guetar oasis, were distinguished by the interesting oil quality compared with Mateur and foreign cultivars. These results offer opportunities for further genetic improvement of pistachio oil quality.
Characterization and gene cloning of a maltotriose-forming exo-amylase from Kitasatospora sp. MK-1785
A maltotriose-forming amylase (G3Amy) from Kitasatospora sp. MK-1785 was successfully isolated from a soil sample by inhibiting typical extracellular α-amylases using a proteinaceous α-amylase inhibitor. G3Amy was purified from the MK-1785 culture supernatant and characterized. G3Amy produced maltotriose as the principal product from starch and was categorized as an exo-α-amylase. G3Amy could also transfer maltotriose to phenolic and alcoholic compounds. Therefore, G3Amy can be useful for not only maltotriose manufacture but also maltooligosaccharide-glycoside synthesis. Further, the G3Amy gene was cloned and expressed in Escherichia coli cells. Analysis of its deduced amino acid sequence revealed that G3Amy consisted of an N-terminal GH13 catalytic domain and two C-terminal repeat starch-binding domains belonging to CBM20. It is suggested that natural G3Amy was subjected to proteolysis at N-terminal region of the anterior CBM20 in the C-terminal region. As with natural G3Amy, recombinant G3Amy could produce and transfer maltotriose from starch.