No abstract

Serine proteinase inhibitor(s) and small amounts of cysteine proteinase inhibitor were detected in both leaf and stem tissue 48 h after mechanical injury to the lower leaf of 21–25 day old tomato cultivars (cv). Leaves accumulated about 2–15 times more trypsin inhibitor than stem tissue. Approximately 10 times more trypsin inhibitor (TIU) accumulated in plants held at 30C in continuous light compared to plants held under ambient greenhouse conditions after injury. Uninjured plants held at 30C under continuous light accumulated less proteinase inhibitor(s) than injured plants. Holding Bonnie Best in the dark at 30C for 48 h resulted in less inhibitor(s) accumulation in response to mechanical wounding than holding plants at 30C in continuous light. TIU/g tissue recovered from injured plants held at 30C under continuous light varied with cultivar, i.e., for leaves: Bonnie Best (33.61), Alta (21.00; 25.43), Castlemart (16.00; 13.17) and Halley (1.96); and for stems: Castlemart (8.29), Alta (4.47) and Bonnie Best (2.59). SDS‐PAGE assayed for inhibitor activity revealed the main trypsin and chymotrypsin inhibitor(s) in injured leaves both had a molecular mass (Mr) of 19.1 KD on SDS‐PAGE substrate gels. Treatment of the inhibitors with 2.0% SDS at 100C prior to electrophoresis revealed a second major trypsin inhibitor (Mr = 16.4 KD) and two additional major α‐chymotrypsin inhibitors (Mr = 16.4; 6.2 KD).

SummaryTwo beverage clouding agents were produced from peels of Valencta orange and of Baladi Lemon. Three enzyme preparations, Pectinex ultra SP-L, Novo Ferm and Ultrazyme 100, were used under their estimated optimum conditions to hydrolyse pectin of the peel. Novo Ferm was proved the optimum preparation to use for preparing the two clouds. The chemical and physical properties of the produced clouds were evaluated. During storage the colour of lemon cloud was more stable than that of orange which showed significant browning. Sensory evaluation of two citrus drink when 5, 10 and 15% of the clouding agents were added, indicated that colour and appearance of drinks were improved. N o bitterness was detected when orange cloud was added up to 15%. The cloudy of the produced drinks was stable after 42 days storage at 25 "C.

The presence of residual endogenous quality-related fruit and vegetable enzymes in either raw or processed fruit or vegetable products may cause loss of quality during processing or storage. The content and properties of such enzymes in these raw sources vary widely with type, species, and variety of the sources and the nature of the environment in which they grew. This study was carried out to determine the optimum conditions (pH and temperature) and total initial activities of three quality-related oxidative enzymes [peroxidase (POD), polyphenol oxidase (PPO), and lipoxygenase, (LOX)] in three fruit varieties; mango (Mangifera indica var. Zebda), banana (Musa cavendishii var. Enana), (peel and pulp), olive (Olea europaea var. Picual) and three vegetables; green beans (Phaseolus vulgaris var. Littel Marvel), tomatoes (Lycopersicon esculentum var. Marmand), cucumber (Cucumis sativus var. Ria) grown in Egypt. The POD, PPO and LOX activities were detected in the six examined homogenates. The optimum pH and temperature values for high enzyme activities were varied according to the type of fruits and vegetables. The highest amount of POD was found in green beans extract (0.207 unit mg-1 protein of the sample) and the lowest amount was for banana peel (0.087 unit mg-1 protein). However, the green beans extract had the lowest content of PPO. In contrast, the highest content was for banana peel. For LOX activity, the mango extract exhibited the greater extent (0.249 unit mg-1 protein) than cucumber and tomato extracts (0.228 and 0.211 unit mg-1 protein, respectively). The activity of LOX was very low in the crude banana pulp homogenate (0.068 unit mg-1 protein).