Submitted to: Journal of Food Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/31/2009
Publication Date: 10/1/2010
Citation: Azhuvalappil, Z., Fan, X., Geveke, D.J., Zhang, H.Q. 2010. Thermal and non-thermal processing of apple cider: storage quality under equivalent process conditions. Journal of Food Quality. 33(5):612-631. Interpretive Summary: Non-thermal processes like pulsed electric field (PEF) and ultraviolet (UV) light are developed as alternative pasteurization technologies to thermal processes to extend shelf life and enhance the microbial safety of fresh juice while preserving organoleptic and nutritional qualities. For fair comparison of the effects on quality of juice, both thermal and non-thermal processes must achieve equivalent reduction in microorganism levels. In the present study the effect of PEF, UV and thermal processes on apple cider quality were compared at conditions optimized to achieve equivalent 6 log reductions of E. 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. The information will help the juice industry to adopt PEF technology to better preserve the freshness of fruit juices.
Technical Abstract: Three processing techniques: heat, pulsed electric field (PEF) and ultraviolet light (UV) were optimized to achieve a similar 6 log reduction of inoculated Escherichia coli K12 in apple cider. PEF treatment at 23 kV/cm for a total treatment time of 150 us at 48C, UV exposure for 51 s at 15C and heat treatment for 1.3s at 76C were the conditions used for processing fresh apple cider for a 4-week storage study at 4C. The effect of treatments on cider quality was investigated based on microbial populations (total aerobic and yeast & mold), sensory, color and physical properties (pH and Brix). 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 & 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 ((CIE 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.