Bioactive compounds and mycotoxins distribution in maize milling fractions.

Maize is dry-milled to produce a range of flours and grits which are further processed for snacks, breakfast cereals and cooked or extruded products. The products and by-products of maize milling processes are the results of a processing that breaks kernel and separates it into its anatomical parts on the basis of the various particle sizes. Maize is an important source of various bioactive compounds (Kurilich & Juvik, 1999), although in the temperate areas this crop is prone to pre-harvest contamination of several mycotoxins, among which fumonisins are the most frequent (Vanara et al., 2009). The aim of this research was to evaluate how the amounts of bioactive compounds and fumonisins of whole kernel is re-distributed between the different processing products. The study was carried on 6 maize homogeneous lots (harvested in growing seasons 2011 and 2012), each one composed by only one hybrid, kept separated from harvest to storage. Kernels of each lot were milled at the same time in an industrial mill employing two types of milling processes, a dry-milling process for the production of maize flours [grits-meal (500-800 µm), fine-meal (350-500 µm), flour (< 350 µm), animal meal, germ] and a de-germing process after conditioning for the production of hominy grits [large (> 4000 µm), medium (2500-4000 µm) and small (1200-2500 µm), animal meal, germ]. Sampling of milling fractions was carried out according to Reg. (EC) No 401/2006. Whole unprocessed kernel and all products and by-products of both milling process were examined for their total Dietary Fibre (DF), Total Phenolic Content (TPC), Total Antioxidant Activity (TAA), Resistant Starch (RS), xanthophylls (XP) contents and fumonisins contamination. Results suggested that bioactive compounds are unevenly distributed in maize kernels and that the distribution pattern is different considering the class of nutrients. Total DF, TPC and TAA were predominant in animal meal and germ fractions. Considering the endosperm the lowest values of TPC and TAA were observed in fractions characterized by the greatest particle size. Specifically, the large hominy grits fraction showed a TPC content about 3-fold lower than whole grain and consequently its TAA was halved. Other bioactive compounds such as RS and XP were predominant in the endosperm fractions. XP content was not influenced by the particle size, while RS was about 3-fold higher in the grits-meal fraction than in the flour one. The animal meal fractions (mainly constituted by the outer layers of the kernels) were most subjected to contamination by fumonisins, whose content was 3-fold higher than in the whole grain. After the milling process the contamination of endosperm products was reduced, and, as reported for TAA and TPC, the lowest contamination was observed in fractions characterized by the greatest particle size.