Use of microwave processing to reduce the initial contamination by Alicyclobacillus acidoterrestris in a cream of asparagus and effect of the treatment on the lipid fraction

The effects of a short-time microwave (MW) treatments on the survival of Alicyclobacillus acidoterrestris spores (105 spores/g) inoculated in a cream of asparagus, along with the oxidation of the fat component (olive oil), were investigated. The samples were MW-treated at 60-100% of power (2450 MHz) for 3-7 min; power and processing time changed according to a Central Composite Design at two variables/five levels. The combinations resulting in a 2-fold reduction in the number of alicyclobacilli spores (100% of power-5 min; 80%-6 min; 80%-7 min) were stored at different temperatures and times (25 °C/27 days, 37 °C/18 days and 50 °C/9 days), to determine the decay of the qualitative characteristics of the lipid fraction. Peroxide value, K232, K270 and Rancimat test (induction time) were chosen as indexes of primary and secondary oxidation. MW-effect on the spores depended upon both the power and the treatment time; moreover the interaction [power] × [time] was the most significant variable. As regards the effect of MW on the lipid fraction, the results suggested that MW affected slightly induction time, peroxide values and spectrophotometric determinations, especially at low powers. Industrial relevance: Since the middle of 1990s, MW-processing has been regarded as a convenient approach for the stabilization of vegetable preserves. In Southern Italy, olive oil is an essential ingredient for this kind of food; however, it is well known that a strong thermal processing as well as not-correct storage could affect it significantly and increase the art of oxidation. This research provides some useful information on the effects of MW for a new product, an asparagus cream, focusing on the influence of this approach on olive oil oxidation, thus suggesting that MW could be a convenient preservation technique. © 2009 Elsevier Ltd. All rights reserved.