The Effect of pH and Temperature on Cabbage Volatiles During Storage

During storage of shredded cabbage, characteristic sulfurous volatile compounds are formed affecting cabbage aroma both negatively and positively. Selected ion flow tube-mass spectrometry (SIFT-MS) was used to measure the concentration of cabbage volatiles during storage. The volatile levels of cabbage samples were measured at pH 3.3 to 7.4 at 4 degrees C for 14d, and pH 3.3 at 25 degrees C for 5d in order to determine the effect of pH and temperature. Aroma intensity, best aroma, freshness, and off odor were evaluated in a sensory test of the samples at 4 degrees C. The desirable volatile allyl isothiocyanate was lower in high pH samples (pH 7.4 and 6.4), whereas higher concentrations were detected in low pH samples (pH 3.3 and 4.6). Lipoxygenase volatiles, which produce a fresh green and leafy aroma in cabbage, were generated in very low amounts at any pH value. High pH samples generated significantly higher concentrations of off odors such as dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, and methanethiol. Sensory tests showed that higher pH samples had significantly stronger off odor and lower desirable cabbage aroma than lower pH samples. Thus, sensory results matched the volatile results in that samples at higher pH levels formed the highest amount of undesirable volatiles and the least amount of desirable volatiles. Storage at 25 degrees C produced similar concentrations of allyl isothiocyanate, but significantly higher levels of off odors, than at 4 degrees C. Shredded cabbage products should be stored in low pH dressings to minimize formation of off odors and maximize formation of characteristic, desirable cabbage odor. Practical Application Low pH samples formed fewer undesirable, and more desirable volatile compounds overall. The natural pH of cabbage is around 6.4, and at this pH, higher concentrations of off odors are formed during storage. Thus, low pH salad dressings are more suitable for storage of ready-to-eat cabbage products in terms of sensory quality, and high temperature is not suitable for cabbage storage, since undesirable aroma compound formation is high, desirable aroma loss occurs quickly, and microbial growth occurs at a very early stage of storage.