dent on tissue temperature at harvest, respiratory activity of the veg-
etable and the possibilities for maintaining the optimum storage tem-
perature along the entire postharvest chain. For production of minimally
processed, refrigerated (MPR) vegetables, it is essential to start with
precooled material and maintain a low temperature during chopping,
washing, packaging and distribution. For such ready-to-eat vegetables
maintenance of a stable temperature is also crucial for avoiding micro-
bial spoilage, and therefore the key to success for consumer-packed MPR
products (Ahvenainen, 1996).
Methods for prediction of shelf life/storage life at constant tempera-
tures have been published for many products (Thorne and Meffert, 1979).
Most shelf-life studies (Labuza, 1982; Shewfelt, 1986) of fresh vegeta-
bles assume that the rate of deterioration according to time is indepen-
dent of the quality level, which gives zero order reactions and linear
relationships between number of days from harvest and quality deterio-
ration (van Beek et al., 1985). However, during distribution and retail-
ing most produce is subjected to irregular temperature regimes. Is it then
possible to estimate the amount of remaining quality at the time a prod-
uct is delivered to the retailer?
Applications of the Time-Temperature-Tolerance method (van Ars-
del, 1957) rest upon the assumption that changes in harvested products
are additive and commutative and that there are no effects of the tem-
perature change itself. “Additivity” means that the total loss of quality
is the sum of the amount of quality lost at each temperature whereas
“commutativity” means that the total amount of quality lost is indepen-
dent of the order of the various temperatures exposed to the product. In
an investigation with tomatoes cv. ‘Nomato,’ Thorne and Alvarez (1982)
were able to demonstrate that color and firmness changes were both ad-
ditive and commutative and could be used to predict the storage life of
tomato fruits under any fluctuating temperature conditions between 12
and 27°C.
Low temperatures enhance the storability and shelf life of most veg-
etables as long as the temperature is above the threshold level for chill-
ing injury or freezing damages of the tissue. For biennial vegetables
long-term storage at a temperature just above zero will lead to vernal-
ization with subsequent regrowth and sprouting when the produce is ex-
posed to long-day conditions during retailing. A similar situation is often
present in Chinese cabbage where vernalization may occur in the field
with a rapid development of an inflorescence inside the cabbage head
(Elers and Wiebe, 1984a, b). Nondestructive methods for detection of
Influences of the Environment 101