Joseph Makhlouf

FREEZE-DRYING CHARACTERISTICS OF STRAWBERRIES

ABSTRACT Drying kinetic, as well as color and volume variation, of whole and sliced strawberries were investigated after freeze-drying under various temperatures (30, 40, 50, 60 and 70°C). Dehydration time increased proportionally to the thickness of the product and heating plate temperature markedly reduced it. Freeze-drying caused a pronunciation in red color of strawberries. A decrease in hue angle by 22.5% (skin) and by 42.4% (pulp) was noted, with no significant effect of freeze-drying temperature up to 70°C. The strawberries had a volume reduction of 8% (whole) and 2% (sliced) due to freeze-drying although the level of shrinkage was also independent of freeze-drying temperature. However, the percentage of collapsed strawberries increased with process temperature. At heating temperatures higher than 50°C, the strawberry dry layer temperature was higher than the estimated glass transition temperature of dried fruit, increasing the risk of collapse.

Distribution of cholesterol in milk fat fractions

Milk fat was fractionated into liquid (m.p. congruent to 12 degrees C), intermediate (m.p. congruent to 21 degrees C) and solid (m.p. congruent to 39 degrees C) fractions by three different processes--melt crystallization, short-path distillation and supercritical CO2 extraction--and the cholesterol content of these fractions determined. Cholesterol was enriched in the liquid fractions from all three processes, in particular about 80% of the cholesterol being found in the liquid fraction obtained by short-path distillation. The basis of migration of cholesterol into various milk fat fractions was explained by its affinity to various triglycerides (melt crystallization) and by vapour pressure and molecular weight (short-path distillation). It was more complex in the supercritical CO2 extraction process; the interplay of cholesterol affinity toward CO2 and its molar volume, and its vapour pressure enhancement under applied pressure play a role.

Fractionation of anhydrous milk fat by short-path distillation

Anhydrous milk fat was fractionated by short-path distillation into four fractions at temperatures of 245 and 265 C and pressures of 220 and 100 μm Hg. Two fractions (LF1 and LF2) were liquid, one fraction (IF) was semi-solid and one fraction (SF) was solid at room temperature. The fractions were characterized by melting temperature profile, solid fat index and triglyceride and fatty acid compositions. The peak melting temperature progressively increased (8.8 to 38.7 C) from liquid to solid fractions. The solid fat content ranged from 0 to 27.5% at 20 C, while native milk fat was 15.4%. The short chain (C24–C34) triglycerides were enriched in the LF1 fraction, long chain (C42–C54) triglycerides were concentrated in the SF fraction, and medium chain (C36–C40) triglycerides in the IF fraction; in the LF2 fraction, though, both short and medium chain triglycerides were enriched. Short chain (C4–C8) fatty acids gradually decreased from liquid to solid fractions and the trend was reverse for long chain (C14–C18) fatty acids, both saturated and unsaturated. The weight average molecular weights and geometric mean-carbon number of milk fat fractions were in the range of 590.7–782.8 and 31.9–46.3, respectively, compared to 729.3 and 41.0, respectively, for native milk fat, suggesting short-path distillation effects a very high degree of molecular weight separation.

Modified atmosphere preservation of freshly prepared diced yellow onion

Abstract The influence of controlled atmosphere storage conditions on the microbiological and sensory quality and the physiology of diced, ‘ready-to-use’ yellow onion was investigated. In the first experiment, diced onion was stored for 14 days at 4 °C and high relative humidity under a continuous stream of nitrogen containing (%O 2 /%CO 2 ): 20/0, 2/0, 2/5, 2/10 and 2/15. The tissue was sampled for microbiological and sensory analysis on days 0, 4, 9 and 14. In the second experiment, the diced onion was stored for 12 days at 4 °C under (%O 2 /%CO 2 ): 20/0, 2/0 and 2/10 treatments. Samples were collected on days 0, 4, 8 and 12 for physiological analysis. The following parameters were studied: mesophile and psychrotroph counts, pyruvate content (an index of flavor intensity), color, sensory quality, rate of respiration and sugar (fructose glucose, sucrose and total sugars) content. CO 2 enrichment of the atmosphere delayed diced onion deterioration. Microbial development was delayed, particularly that of the psychrotroph flora. Sensory quality was optimal under the 2% O 2 /10% CO 2 atmosphere. However, pyruvate and color determination showed no noticeable difference between treatments, although the period of storage significantly influenced these parameters. High CO 2 and low O 2 delayed the rise in respiration and the reduction in sucrose content, as compared with the control in air. Levels of reducing and total sugars remained constant throughout storage under all treatments. Browning after cooking developed with increasing length of storage, but was delayed by storage under 10% CO 2 . Involvement of sugars in this disorder is discussed. This work provides a basis for the development of modified atmosphere packs which will extend the preservation of the product for 2 weeks.

Effects of UV-C irradiation on lipid peroxidation markers during ripening of tomato (Lycopersicon esculentum L.) fruits

The effects of a hormic dose (3.7 kJ m−2) of UV-C (254 nm) on changes in fruit membrane lipids perox-idation markers during storage were determined using tomato (Lycopersicon esculentum L. cv. Trust) fruit. There were two distinct response phases following the treatment. A significant induction of lipid peroxidation markers (lipofuscin-like compounds, malondialdehyde, aldehydes, pentane, ethane, hydrogen peroxide, and efflux of elec-trolytes including potassium and calcium) occurred within the first 5 days. This induction suggests that the cell mem-brane was the primary target of UV-C irradiation. After this period, the level of all of these peroxidation markers become lower in UV-C-treated fruit than in control fruit, suggesting the induction of a defense or repair mechanism, probably involving production of antioxidants and activation of antioxidative enzyme. Within the second phase, any changes in lipid peroxidation activity reflected the fruit ripening / senescence process rather than the UV-C effect.

Storage of broccoli florets in ethanol vapor enriched atmospheres

Abstract Broccoli florets are highly perishable because the buds turn yellow rapidly. Exposure to an atmosphere enriched in ethanol vapor increased their storage life. The florets exposed to ethanol levels of 500, 1000 and 2500 ppm (± 10–15%) retained higher levels of chlorophyll than the control (0 ppm) stored for six days at 13 °C under water-saturated air. A level of 2500 ppm of ethanol in the atmosphere completely inhibited mold growth. A continuous treatment at 13 °C for six days with 2500 ppm did not have any effect on the floret respiration rate. In addition the weight loss of florets exposed to ethanol was significantly lower than that of control. However, this treatment induced undesirable off-odors in stored broccoli, presumably due to a high accumulation of ethanol and acetaldehyde in the tissue. On the other hand, shorter exposure to ethanol (12–24 h) with 2500 ppm of ethanol at 13 °C followed by air storage at 13 °C slowed down the loss of chlorophyll, compared to the control, and prevented the induction of off-odors in broccoli florets. Moreover, internal levels of ethanol and acetaldehyde of pre-treated buds decreased during six days of storage compared to the continuous treatment. It appears that a pre-treatment with ethanol vapor as an adjunct to moderate-temperature storage can be useful in the storage of broccoli.

Fractionnement de la matière grasse laitière par cristallisation simple et son utilisation dans la fabrication de beurres mous

Abstract Anhydrous milk fat was fractionated into 7 fractions by melt crystallization at temperatures ranging from 26°C to 9°C. The fractions were characterized by fatty acid and triglyceride composition, melting point profile and solid fat index. The process was based on a slow cooling of the melted fat, a short duration of stabilization at the fractionation temperature and the separation of the crystals from liquid phase by vaccum filtration. The liquid fractions were rich in smaller triglycerides as well as short chain and unsaturated fatty acids, whereas the solid fractions had high concentrations of larger triglycerides with long chain saturated fatty acids. The separation of milk fat triglycerides by molecular size is not feasible by melt crystallization as evidenced by the weight average molecular weight of various fractions ranging from 714,8 to 769,7 compared to 727,5 for native milk fat and the geometric mean-carbon number of fractions ranging from 38,4 to 44,9 compared to 41,0 for milk fat. Selected fractions were used for the preparation of spreadable butters which were characterized for their spreadability, melting temperature profile and dilatation. Experimental butters showed a 2 to 4 fold improvement in spreadability at 7°C compared to the regular butter and they approached the spreadability of soft margarine at 15°C. Butter made from a blend of 80% of liquid fraction obtained at 9°C and 20% of solid fraction, obtained at 26°C, was the most spreadable. The limitation in improving spreadability of butter from milk fat triglycerides alone, is discussed.

Drying of Garlic (Allium sativum) and Its Effect on Allicin Retention

Convective hot air-drying and freeze-drying were investigated as potential processes to preserve and concentrate allicin in garlic. Both temperature and air velocity had an important effect on hot air-drying kinetics. Sample size and temperature significantly affected the duration of freeze-drying, and thus the remaining moisture content of the garlic samples. Allicin content decreased with an increase of drying temperature in both convective hot air-drying or freeze-drying. Moderate air temperatures (40 and 50°C) allowed a better allicin retention than higher temperatures (60°C). However, retention of allicin was more important in garlic samples freeze-dried at a temperature of 20°C. The drying method did not show a significant impact on glass transition temperature values, indicating that garlic composition is a more important factor than internal structure. The predictions of the Gordon and Taylor model are in good agreement with the experimental data.

Biosynthesis of sulfur volatile compounds in broccoli seedlings stored under anaerobic conditions

Abstract Sterile broccoli seedlings were used to investigate the effects of anaerobic atmosphere on biosynthesis and emission of sulfur volatile compounds which are responsible for off-odors in controlled and modified atmosphere stored broccoli. The identification of methanethiol, dimethyl sulfide, dimethyl disulfide and hydrogen sulfide in the head space of anaerobically stored broccoli seedlings confirmed that undesirable odors in broccoli are of plant origin. Evidence in support of the enzymatic origin of these volatiles was also obtained by using aminooxyacetic acid which is a potential inhibitor of pyridoxal phosphate-dependent enzymes; the production of sulfur volatiles was delayed and reduced by more than 95%. However, an anaerobic atmosphere had no inducible effect on the activities of cystine lyase, S-alkylcysteine lyase and cysteine desulfhydrases. These pyridoxal phosphate-dependent enzymes are thought to be involved in the production of volatile sulfur compounds by catalyzing the respective breakdown of cystine, cysteine and S-methyl- l -cysteine. The results suggest that these enzymes are not limiting factors in the production of sulfur volatiles in broccoli. However, the analysis of the contents of free sulfur amino acids and their derivatives showed an important increase in potential substrates for the synthesis of volatile sulfur compounds such as cysteine, methionine and S-methylcysteine as a result of anaerobic treatment. This increase usually preceeded or corresponded with the increased emission of sulfur volatiles. Results obtained by monitoring individual free amino acid content variation as a function of storage time, under anaerobic conditions, suggested enhanced conversions among sulfur amino acids. Other sources of sulfur amino acids, such as protein degradation and de novo synthesis, might explain the increase in these amino acids under anaerobiosis.

Some nutritional characteristics of beans, sweet corn and peas (raw, canned and frozen) produced in the province of Quebec

Abstract A three-year study was conducted to assess some nutrient contents of beans, sweet corn and peas (raw, canned and frozen) produced by four processing plants in the province of Quebec. Nutritional analysis were conducted on vitamin C, riboflavin, thiamin, minerals (Ca, Mg, K, Na, Fe) and fibers (solubles, insolubles and total). Results showed that the nutrient contents of raw and processed vegetables were quite different from those reported in the USDA Handbook no. 8–11. The differences were mainly due to vitamin C and mineral contents. Results also showed that raw vegetables when boiled under optimal conditions have nutrient contents similar to frozen vegetables and superior to canned vegetables. Among minerals Na was the most variable, probably due to variation in recipes from one processing plant to another. Na contents of canned vegetables were lower than the average values in the USDA tables. The study also provides new information on nutritive values of canned corn-on-the-cob which was not listed in USDA tables, and generates new nutrient data such as fibers (solubles, insolubles and total contents) to update the present food composition tables.