Relationships between storage quality attributes, such as russet spotting and browning intensity, and physiological attributes, such as soluble phenolic content and polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities, of minimally processed crisphead lettuce (Lactuca sativa L.) were studied. The processed lettuce tissue was kept in air or air plus ethylene at 2 or 5 μl·liter-1 at 2.5 or 5C for 1 to 4 days and then transferred to air at 2.5, 5, or 20C for 1 to several days. None of the above physiological attributes of the initial samples from eight lettuce cultivars (Calmar, El Toro, Sea Green, Pacific, Monterey, Salinas 88, 86-13, and Nerone) and three maturity stages (immature, mature, and overmature) correlated with their storage quality. However, ethylene-induced PPO and PAL activities and browning intensity measured 3 to 4 days after harvest consistently and significantly correlated with the final visual quality of the ethylene-treated, minimally processed lettuce after 6 to 10 days of storage. Among these three attributes, ethylene induced a 2.5- to 5.3-fold increase in PAL activity, while the relative changes in PPO activity and browning intensity were only 23% to 68%. Ethylene-induced PAL activity possibly may be used as an index to predict the storage life of minimally processed lettuce.
The composition and quality of edible tender stems or cladodes of 3 Prickly Pear Cactus species (Opuntia amyclaea, O. ficus-indica, and O. inermis) were studied at different stages of development. This traditional Mexican vegetable is called "nopalitos" in Spanish and "cactus leaves" in English. Cladodes harvested when 20 cm in length have the following average composition per 100 g: 91.7 g of water, 1.1 g of protein, 0.2 g of lipid, 1.3 g of ash, 1.1 g of crude fiber, 4.6 g of complex carbohydrates and 0.82 g of simple sugars, 12.7 mg of ascorbic acid and 28.9 micrograms of carotenes. The cladode's juice has an average pH of 4.6, 0.45% titratable acidity and 6.9% soluble solids. The components which varied most during development of the cladodes were: carotenes, acidity and total carbohydrates which increased, and protein and crude fiber (acid-detergent) which decreased. The nutritive value of the tender cladodes in the stages of growth at which they are commonly harvested and consumed (15 to 25 cm long weighing 50 to 80 g per stem), was similar for the 3 species.
Volatiles were isolated from broccoli stored under controlled atmospheres containing different levels of N2, O2, and CO2. The volatiles were analyzed by capillary GLC and MS. The presence of the previously identified methanethiol, ethanol, ethyl acetate, and dimethyl disulfide in low oxygen stored broccoli was confirmed. Additional compounds, identified in the present work, increasing under these low oxygen conditions included 3-hydroxybutan-2-one, methyl thiocyanate, hexanal, (£)-2-hexenal, 3-methylbutanol, dimethyl trisulfide, and 21 other compounds. Major compounds include methanethiol, ethanol, ethyl acetate, 3-hydroxybutan-2-one, and methyl thiocyanate. The combination of threshold and concentration data indicated that the major contributors to the odor of the objectionable samples included methanethiol, dimethyl trisulfide, and /3-ionone.
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