Combined effects of intermittent radio frequency heating with cinnamon oil vapor on microbial control and quality changes of alfalfa seeds

Abstract

Alfalfa sprouts have high nutritional values when consumed raw, but are easily contaminated by food pathogens. This study aimed to evaluate effects of essential oil (EO) vapors, RF heating and their combinations on microbial inactivation, germination rate and generated sprouts' quality of alfalfa seeds at moisture contents of 7.52%, 9.53% and 11.45% wet basis (w.b.). Results showed that cinnamon oil and oregano oil vapors both had antimicrobial effects against Salmonella on alfalfa seeds and cinnamon oil vapor had a little better activity. Weibull model well fitted the Salmonella inactivation curves under RF heating. The rate of Salmonella inactivation increased but germination rate decreased with increasing temperature and moisture content of seeds. The intermittent RF treatments improved the heating uniformity and germination rate of the whole batch of seeds as compared to the continuous RF heating. The combination of intermittent RF heating and cinnamon oil vapor exhibited additive antimicrobial effects, up to 3.99-4.12 log CFU/g Salmonella reductions, and maintained the germination rate above 90%. However, for natural microbial decontamination, combined treatments only caused 0.56-0.82 log CFU/g reductions of total bacterial counts. The fresh weight, length, flavor, the content of phenolics and ascorbic acid, and antioxidant capacity of generated sprouts were not significantly impacted. The study provided an effective method for microbial control on sprouting seeds.

Keywords: Alfalfa seed germination; Cinnamon oil vapor; Combined treatment; Radio frequency heating; Salmonella inactivation; Sprout quality.