THERMAL AND NONTHERMAL PROCESSING OF APPLE CIDER: STORAGE QUALITY UNDER EQUIVALENT PROCESS CONDITIONS

Abstract

ABSTRACT Three processing techniques: heat, pulsed electric field (PEF) and ultraviolet (UV) light were optimized to achieve a similar 6 log reduction of inoculated Escherichia coli K12 in apple cider. Microbial populations (total aerobic and yeast and mold), sensory, color and physical properties (pH and°Brix) of processed apple cider were investigated during 4‐week storage at 4C. PEF and thermally processed cider maintained good microbial quality during 4 weeks of storage while UV‐treated cider showed a significant (P < 0.05) growth in yeast and mold after 2 weeks of storage. As a result,°Brix value decreased significantly (P < 0.05) for UV cider after 4 weeks of storage. Apple cider pH was neither affected by any treatment nor by storage. Thermal and UV‐pasteurized ciders faded significantly (P < 0.05) during storage (International Commission on Illumination L*[lightness] and b*[yellow] values increased) compared to PEF cider. Triangle sensory analysis indicated a significant difference (P < 0.05) in aroma between treatments. PEF‐treated cider was preferred over thermal and UV cider by sensory panelists at the end of the storage period. The results suggested that PEF‐treated apple cider had a longer shelf life than UV‐treated cider and a better aroma and color than thermally processed sample.PRACTICAL APPLICATIONSNonthermal processes like pulsed electric field (PEF) and ultraviolet (UV) light are developed as alternative pasteurization technologies to heat for their efficacy to extend shelf life and enhance the safety of fresh juice while preserving organoleptic and nutritional qualities. For fair comparison of the effects on quality of juice, both thermal and nonthermal processes must achieve equivalent reduction in microorganism levels. In the present study, the effect of PEF, UV and thermal techniques on apple cider quality are compared at conditions optimized to achieve equivalent 6 log reductions in Escherichia coli. Our results showed that PEF extended the shelf‐life of apple cider by inactivating spoilage microorganisms compared to UV processing, and better preserved the freshness (aroma and color) over traditional thermal processing. Based on these results, PEF process is the best choice among the three technologies studied.