Potential use of microwave treatment on fresh-cut carrots: Physical, chemical and microbiological aspects

BACKGROUND: The effect of microwave treatments (900 and 750W for 45 and 60s) on the microbial, physicochemical and sensory properties of fresh-cut carrot slices and the contents of several bioactive compounds was studied. Carrot samples were stored for 7 days at 5°C. RESULTS: The microwaving of fresh-cut carrots reduced the initial respiration rate (8.6 CO2 mL kg-1h-1) by 55-74% compared with untreated samples, although the rates then increased during storage. The initial pH (6.7), titratable acidity (0.036%), soluble solid content (8.2 °Brix) and shelf-life of the samples did not differ greatly from those of the untreated samples. Microwaving prevented the incipient whitening and surface dryness during storage. In general, no significant changes in phenylalanine ammonia lyase activity (5.5μmol t-cinnamic acid kg-1h-1), total phenolics (TP, 81.3mg chlorogenic acid equivalent kg-1 fresh weight (FW)) or total antioxidant capacity (TAC, 74.2μmol Trolox equivalent kg-1 FW) were observed on the processing day or over storage. However, the mildest treatment (750W for 45s) caused TP and TAC enhancements of 118 and 394% respectively after 7 days of shelf-life. Microwave treatments reduced the initial microbial loads of the samples by up to 1.8 log units, although their microbial growth was greater than that of the untreated samples throughout storage. CONCLUSION: Mild microwave treatments such as 750W/45s and 750W/60s are a good sustainable alternative to the use of NaOCl; however, combining them with other sanitizing techniques is needed to control microbial growth throughout the shelf-life of fresh-cut carrot slices.