POSTHARVEST STORAGE RESPONSE OF CABBAGE SUBJECTED TO VARIOUS DIURNAL FREEZE-THAW REGIMES

Recent research has established criteria for long term (8–9 months) commercial CA storage of cabbage Brassica oleracea L. and compared it with refrigerated air (RA) storage. Only the best quality cabbage should be utilized to obviate deterioration and decay problems caused by various factors, including freezing injury. This study investigated the effects of 12 freeze-thaw regimes on cv. Evergreen Ballhead stored for over 8 months in CA (5% CO₂, 2.5% O₂ remainder N₂) and RA environments at 0.6°C.

Cabbage which was seeded directly into pots and grown to maturity in both greenhouse and field conditions was subjected to natural (-4.4°C min for 3 and 6 freeze cycles) and simulated (1 through 5 freeze cycles with mins of -1.7, -2.8, -3.9°C; and deep freeze to -9.4°C over 8 hours) conditions. An untreated check was used. A programmable chamber with a simulated soil heat source was used to produce an asymmetric sinusoidal simulation of typical late fall harvest conditions in Central New York State and the deep freeze exposure. All exposures were made using mature intact plants attached to undisturbed soil masses.

281 specimens were stored in CA and RA conditions and sampled at 73, 133, 193, and 253 days. Exposures (cumulative °C-hours below the cell freezing point, taken as -0.83°C) varied from 15 to 77°C-hours. Small and large heads were exposed, ranging from an average head weight of 909 to 4088 grams, with an absolute range of 527 to 6259 grams. Heads were planted in a greenhouse for regrowth studies immediately after removal and inspection.

The threshold of exposure appeared to be beyond a freeze "severity"/ "exposure" index of -9.4°C/68°C-hours, or -4.4°C/77°C-hours. No immediate visible external or internal freeze-induced damage indicators were evident in either the CA or RA heads, even when specimens were frozen to -1.1°C at the head center. CA cabbage emerged with green color, excellent flavor, and little decay. CA cabbage exhibited progressive yellowing and decay of outer leaves. Some specimens failed to grow when planted or initiated growth, then decayed, especially those subjected to -9.4°C. Almost all others grew, and many flowered or formed new heads.