AN ENDO-POLYGALACTURONASE IN CUCUMBER FRUIT1

A homogenous endo-polygalacturonase (EC 3.2.1.15,) has been isolated from mature pickling cucumbers. This is the first report of an endo-polygalacturonase in cucumbers. The enzyme was purified by three chromatography steps on Sephadex cation exchangers. The molecular weight is 35,000 daltons. With polygalacturonic acid as the substrate at an ionic strength (μ) of 0.15, the pH optimum is 5.6. The enzyme is not active atμ= 0.027. Maximum activity occurred atμ= 0.2. The half-life of the enzyme is 1.2 min at 70°C in pH 5.2, 0.1 M acetate buffer. An inhibitor, isolated from the sericea lespedeza, which inhibits polygalacturonases from fungal sources, also inhibits the cucumber enzyme. This enzyme may be involved in tissue breakdown during the latter stages of fruit development.     

METHOD FOR DETERMINATION OF FIRMNESS IN CUCUMBER SLICES1

A punch and die assembly was adapted to the Instron UTM for deter-mination of firmness of mesocarp and endocarp tissues in cucumber slices. A cylindricalpunch 0.315 cm diameter (0.200 to 0.635 cm diameter tested) and a cucumber slice thickness of at least 0.48 cm were found to be suitable for the method developed. Penetration force was about five times greater for mesocarp than endocarp in 4 to 5 cm diameter cucumbers. Mesocarp and endocarp were firmer near the stem end than near the blossom end of cucumbers. Force readings also declined for both tissues with increase in fruit diameter from about 2 to 6 em. Single slices taken from the center of 20 cucumbers and punched once each at specified locations in the mesocarp and endocarp provided sufficient sampling to limit the coefficient of variation to about 5%. The correlation coefficient between sensory analysis for firmness and puncture force readings of fermented cucumber slices was 0.88.     

INFLUENCE OF THE SKIN ON PUNCTURE PROPERTIES OF CHILLED AND NONCHILLED TOMATO FRUIT

The puncture properties (firmness, toughness) of tomato skin and its influence on the overall puncture properties of mature-green fruit during ambient temperature (22C) ripening or chilled (5C) storage were estimated from the difference between whole fruit puncture force-deformation behaviour and that measured with the skin removed. Although the firmness of the skin of nonchilled fruit did not change significantly (p > 0.05) over 28 days of ripening, its contribution to overall puncture firmness increased from about 25 to 70%. Both skin toughness and its contribution to overall puncture toughness doubled within the first week of ripening of nonchilled fruit. The firmness of chilled fruit skin decreased (p > 0.05) only after 16 days of storage, but its contribution to overall puncture firmness remained constant at 25–30%. Both the toughness of the skin of chilled fruit and its contribution to overall puncture toughness remained constant during storage. Possible artifacts in the measurement of puncture properties of chilled fruit are discussed. The results are consistent with a toughening of tomato skin during early stages of ripening of nonchilled fruit that somewhat compensates for a rapid reduction in pericarp tissue integrity, and with an increase in firmness or rigidity of tomato skin and underlying tissue(s) during chilled storage of fruit.     

ZJS88－1型杏仁软皮脱皮机的研制

杏仁是人们喜爱的营养保健食品，杏仁软皮的脱除是杏仁加工中要解决的关键问题。本文论述了杏仁软皮的摩擦脱除机理，介绍了ＺＪＳ８８－１型杏仁软皮脱皮机柔性硬摩擦装置及脱皮机结构材点。生产试用及其机器性能测试结果表明：该脱皮机结构合理，性能良好，并适用于类似食品的脱皮加工，具有较广的使用价值。     

IDENTIFICATION OF PROCYANIDIN A2 AS POLYPHENOL OXIDASE SUBSTRATE IN PERICARP TISSUES OF LITCHI FRUIT

Postharvest browning of litchi fruit results in short shelf life and reduced commercial value. Experiments were conducted to separate, purify and identify polyphenol oxidase (PPO ) substrates that cause litchi fruit to brown. PPO and its substrate were extracted from the pericarp tissues of litchi fruit. The litchi PPO substrate was purified using polyamide column, silica gel column and Sephadex LH‐20 column chromatography. The browning substrate was selected by a 0.5% FeCl₃ solution and then identified using a partially purified litchi PPO. Analyses of ultraviolet spectrometry, nuclear magnetic resonance and electrospray ionization mass spectrometry indicated that the PPO substrate was procyanidin A2. The substrate can be oxidized to ο‐quinones by litchi PPO and then form brown‐colored by‐products, resulting in pericarp browning of harvested litchi fruit.     

果蔬保鲜膜的保鲜机理与研究进展

综述果蔬保鲜膜的保鲜机理,介绍果蔬保鲜膜先后出现的硅窗调气薄膜、微孔果蔬保鲜膜、可食性果蔬保鲜膜、抗菌保鲜膜的主要性能、特点及其应用现状,并简要分析果蔬保鲜膜今后的发展趋势。     

LIPIDS IN SUBCUTANEOUS TISSUES AND LONGISSIMUS MUSCLES OF FEEDLOT AND GRASS-FED EWES1

Subcutaneous and intramuscular lipids from feedlot-and grass-fed ewes were studied to determine if diet would influence fatty acid composition of these older animals. Subcutaneous lipid of ewes from the feedlot-fed group contained more 4-methyl branched acids, less iso and anteiso branched acids, less stearic acid and more octadecenoic acid than grass-fed ewes. Only small amounts of medium chain acids (10–15 carbons) were noted in longissimus muscle lipids from both dietary groups and essentially all of them were in the triglycerides. Lipids in longissimus muscle of feedlot ewes contained more monounsaturated and less polyunsaturated acids and this was due to higher levels of triglycerides in longissimus lipid of feedlot-fed ewes. Approximately three times as much high melting stearic acid was present in subcutaneous lipid of both dietary groups of ewes as has been noted in subcutaneous lipid of lambs. Reduction of high melting stearic acid in mutton fat by a short grain feeding period should make mutton more acceptable.     

高效液相色谱法测定蜜饯中食用合成色素

建立了蜜饯中食用合成色素（柠檬黄、苋菜红、胭脂红、日落黄、亮蓝）的高效液相色谱测定方法，采用C18（4.6mm×200mm，5μm）色谱柱，甲醇和乙酸铵为流动相，流速为1．0mL/min，柱温30℃，梯度洗脱程序为：甲醇＋0．02mol／L乙酸铵，6％～40％甲醇，2．8％／min；40％～60％醇，2．5％／min；60％甲醇，3min；6％甲醇，7min；检测波长：0min～5．5min，430nm；5．51min～8．0min，520nm；8．01min-10．0min，510nm；10．01min-13min，480nm；13．01min-20min，600nm。确定了蜜饯中合成色素的前处理方法。本方法具有灵敏度高，干扰少，色素回收率高的优点。     

MINERALS AND XENOBIOTIC RESIDUES IN THE EDIBLE TISSUES OF WILD AND POND-RAISED LOUISIANA CRAYFISH1

The popularity of Cajun cuisine has promoted the consumption of Louisiana crayfish, Procambarus clarkii. Tail meat and hepatopancreatic tissues of crayfish captured from two locations in the Atchafalaya River Basin and four open ponds were analyzed separately for xenobiotic metal and mineral composition using an inductively coupled plasma emission spectrometer (ICP) and chlorinated hydrocarbons by gas chromatograph (GC) with electron capture detector. Less than 3 mg/kg of toxic xenobiotic metals were found in the tail meats and less than 5 mg/kg in the hepatopancreatic tissues. Mineral concentrations were similar to those reported for other crustacean species. Occasional trace amounts of DDD and DDE were found present in tissue samples.     

DISTRIBUTION OF OCHRATOXIN A IN CHICKEN TISSUES AND EGGS

The kinetics of distribution of ochratoxin A (OA) in chicken tissues was studied. Day-old chicks were fed a starter diet alone or containing 1 ppm OA. After 5 weeks, all chicks were intubated with 50 μg ³H-OA per chick. The highest level of radioactivity was found in kidney and liver 8 hr after intubation. Peak levels of OA in kidney, liver and breast were found to be 12, 4, and 0.2 ppb, respectively. Over 90% of the radioactivity was eliminated 48 hr after intubation. Moreover, when laying hens were fed a diet containing 0.5 or 5.0 ppm of OA for 2 weeks, the highest levels of OA were found in the kidney (124 ppb) and liver (80 ppb) also. Levels of OA in breast, leg and eggs of laying hens were found to be 8, 7, and 2.8 ppb, respectively.     

RAPID MESOCARP CELL ELONGATION ENHANCES GUMMING SYNDROME IN JAPANESE APRICOT (PRUNUS MUME SIEB. ET ZUCC.) FRUIT

ABSTRACT

Japanese apricot (Prunus mume Sieb. et Zucc.) ‘Benisashi’ fruit tends to show the physiological disorder of a gumming syndrome, while the fruit known as ‘Nanko’ rarely show this. The accumulated gum becomes a solid gel during the processing period and the commercial value of the mume pickle is consequently decreased. In the present experiment, gum accumulation in the mesocarp tissue and the cell size of the tissue during fruit growth were observed in the two cultivars. In mid‐May, the initiation of the gum duct was observed in vascular bundles in the mesocarp tissue of the two cultivars and plant gum was then observed to accumulate in the duct. No difference in these phenomena was observed between the cultivars until late May. Thereafter, ‘Benisashi’ developed a gum lump visible to the naked eye during Stage III, while the gum lump of ‘Nanko’ did not develop to the visible size as shown in ‘Benisashi’; the lumps could not be confirmed with the naked eye until the mature stage. ‘Benisashi’ showed more rapid fruit growth compared with ‘Nanko’ during Stage III due to explosive mesocarp cell elongation close to the endocarp. Moreover, the rate of gumming fruit of ‘Benisashi’ was higher in bigger fruits than smaller ones. These results indicate that the peculiar cell growth of ‘Benisashi’ fruit may accelerate gum lump formation.

PRACTICAL APPLICATIONS

Gumming syndrome affects the quality of mume pickle. In this experiment, we investigated the mechanisms of gum accumulation in fruit flesh. ‘Benisashi’, which frequently shows the gumming syndrome, presented rapid inner mesocarp cell growth on fruits developing Stage III. This peculiar cell growth may accelerate gum lump formation. Therefore, we have to prevent the cultivational misconduct that induces rapid fruit growth in this period to suppress the gumming syndrome and to increase the commercial value of mume pickle. Moreover, this knowledge is also important in order to breed the new cultivars which do not contain the gumming syndrome.