Storage and Processing Effects on Delivery of Provitamin A Carotenoids from Biofortified Maize
Vitamin A Deficiency (VAD), along with iron and zinc deficiency are considered top global health challenges, with more than 190 million preschool-age children, and 19.1 million pregnant women affected globally (World Health Organization, 2009). Blindness, anemia and infant mortality are some of the devastating consequences of VAD and as such, aggressive and transformative strategies are needed to overcome this nutritional challenge. Biofortification and other nutritionally-sensitive breeding techniques have been promoted as tools to combat VAD by virtue of their ability to increase the natural content of provitamin A carotenoids (pVAC) in maize and other staple crops. The effectiveness of these breeding techniques is often measured by the pVAC content in the final processed food product made from biofortified crops. However, information regarding specific degradation mechanism, relative kinetics of degradation, the impact of traditional and industrial food processing on retention and bioaccessibility of pVAC form maize based foods remains limited. With this in mind, the objective of these studies was to evaluate the impact of storage and processing effects on the delivery of pVACs from biofortified maize genotypes. The first study examined post-harvest stability of carotenoids in kernels of biofortified maize under controlled environmental stress. Kernels from six biofortified maize genotypes were collected at various developmental stages and placed in controlled storage conditions (12-months period), including elevated temperatures and relative humidities. There were no significant changes in the content of individual carotenoids within genotypes during kernel development from 45 days after pollination through the time of harvest. Carotenoid losses through traditional grain drying were also minimal (<9%). However, biofortified maize genotypes showed 40%, 70% and 80% losses of pVAC after 3, 6 and 12 months at controlled storage conditions (60% RH, 22.5 °C), respectively. Carotenoid stability in intact maize kernels was dependent on both temperature and humidity, with some variation observed among genotypes. Additionally, a dent-type genotype (C17xDE3) showed a degradation rate 2 times faster in comparison to all flint-type genotypes evaluated in this study (P < 0.001). In a second study, we evaluated the impact of industrial dry-milling and extrusion processing on carotenoids stability from biofortified maize genotypes. Degermination of biofortified maize kernels resulted in ~10% loss of their total carotenoid content. Dry-milled products of Orange ISO selected A and Hi27xCML328 genotypes showed a ~28% pVAC loss after 90-days storage at controlled storage conditions (11% RH, 22.5 C). Genotype C17xDE3 (dent-type), with the highest pVAC content among genotypes evaluated, showed 68% of pVAC loss after 90-days storage. In addition, these dry-milled by-products showed three times higher rate of carotenoid degradation compared to intact whole kernels from same genotypes. Extrusion cooking showed a great potential to produce maize by-products with a retention of 70-93% of the pVAC content. These data suggested that more in depth study of processing effects are needed to establish impacts to storage and bioaccessibility of pVAC from these extruded maize products. The third study evaluated the impact of fermentation processing commonly leveraged at village level in developing countries on stability and bioaccessibility of pVACs from biofortified maize ogi porridges (a traditional fermented African preparation). Fermentation produced a modest effect (<18% loss) on total carotenoid stability during short steeping periods (<72 h). However, after a long steeping period (120 h) a more dramatic reduction of total carotenoids (63.4%) was observed suggesting an optimal period for retention would be short fermentation time. On the other hand, bioaccessibility of pVACs from fermented maize porridges ranged 1.3-2.3%, with significant differences observed among genotypes (p < 0.05), but not fermentation time. Additionally, fermentation of intact whole kernels, from biofortified genotypes, resulted in modification of final viscosity of fermented porridges that might potentially impact product sensory characteristics and even pVACs bioaccessibility. Overall, these results suggest, that despite efforts to enhance pVAC content on maize genotypes through biofortification, factors including postharvest handling as well as traditional and industrial processing, can serve to alter the delivery of health-promoting carotenoids and more specifically pVAC carotenoids form maize based foods. While increasing carotenoid content of maize remains a focus of biofortification programs, these results suggest that enhancing carotenoid content alone does not guarantee carotenoid content or bioaccessibility through the processing chain or in finished products. As such, future efforts should place equal focus on processing factors and bioavailability assessment to optimize pVAC delivery from these grains.
Ferruzzi, Purdue University.
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