Development and validation of a micromethod for fast quantification of antimicrobial 5-n-alkylresorcinols in grains and whole grain products.

DA SAMPIETRO, ME ARISTIMUÑO FICOSECO, MM BELIZAN, MA VATTUONE, CA CATALAN

Buenos Aires

Congreso; XI Congreso Latinoamericano de Microbiología e Higiene de Alimentos. VI Congreso Argentino de Microbiología de Alimentos y III Simposio Argentino de Conservación de Alimentos (MICROAL 2012).; 2012

Asociación Argentina de Microbiología

The 5-n-alkylresorcinols (5nARs) are food grade antimicrobials located in the outer layers of winter cereal grains. Analyses of 5nARs  indicate the quality and preservation during storage of grain and whole-grain food products. Fast analysis of  5nARs is strongly restricted by the methods currently available. The aims of this work were:1)to develop a micromethod for quantification of 5nARs using Fast Blue RR (FBRR), 2)to validate the use of this micromethod in cereal grains and whole-grain products, 3)to detect interspecific differences in relative contents of 5nARs homologues in such matrices.  Grains of bread wheat (Bio INTA 3004,Baguette Premium,Themix-L), durum wheat (Buck Platino,Buck Cristal), soft wheat (Entrada 6,Entrada 4) and rye (Fausto,Camilo,Lisandro) were provided by INTA Marcos Juarez (Cordoba).Maize hybrids(Avant,Chaltén,Condor),wheat brands,wheat brand products(breads, cookies),semolated cookies and polentas were purchased in the local market.Intact grains (1g), ground grains (1g) or ground food products (10g) were extracted with ethyl acetate. Each extract was filtered, evaporated to dryness, and dissolved in 2 ml of methanol, before use  for colorimetric reactions in 96-well microplates. The micromethod was optimized for basificant agents(K2CO3,NH3, Na2CO3),alcoholic media (ethanol,methanol,butanol,propanol),and concentration of FBRR.The content of 5nARs was determined using both the new micromethod and a Fast Blue B (FBB) method. The  relative composition of 5nARs was determined by GC-MS. Data were subjected to one way ANOVA and LSD test (P=0.05). The optimized method (0.025% FBRR in ethanol, 5% K2CO3) required less time for completion (15 minutes) than the FBB method, with similar sensitivity and selectivity. Contents of 5-n-ARs were ~120-260 µg/g for bread, soft and durum wheat grains and ~340-480 μg/g for rye grains. No 5-n-ARs were detected in maize grains. Interspecific differences were observed in relative composition of 5nARs homologues both in grains and in the whole-grain products.Wheat brand showed the highest levels of 5nARs (470 μg/g), followed by breads (204-300 μg/g) and wheat brand cookies (30-35 μg/g). The 5nARs were absent in polentas and semolated cookies.The composition of 5nARs homologues was the same in wheat grains, wheat brand and their derived breads and cookies. The new micromethod showed a reliable quantification of the antimicrobial 5nARs in grains and whole-grain products.