Karen Smet

Lipid and Protein Oxidation of Broiler Meat as Influenced by Dietary Natural Antioxidant Supplementation

Natural tocopherols (TC), rosemary (RO), green tea (GT), grape seed, and tomato extracts were supplemented in single and in combinations at total concentrations of 100 and 200 mg.kg(-1) of feed in a 4% linseed oil-containing diet to investigate the oxidative stability of broiler breast muscle. Supplementation with 300 mg.kg(-)1 of synthetic antioxidants alone and synthetic antioxidants with alpha-tocopheryl acetate at a concentration of 200 mg.kg(-1) (100 IU) feed was used as a control. Fresh patties were prepared and stored under light at 4 degrees C. After freezing for 8 mo and overnight thawing, 3 other patties were prepared and similarly stored under light at 4 degrees C. During display, samples were evaluated for oxidative stability measurements. For lipid oxidation, the treatment with synthetic antioxidants and 200 mg.kg(-1) of alpha-tocopheryl acetate yielded the lowest TBA reactive species (TBARS) values. For TC, grape seed, and tomato extracts, TBARS values for 100 mg.kg(-1) were higher (P < 0.05) than 200 mg.kg(-1) treatments, whereas no differences (P > 0.05) in TBARS values were observed for RO between 100 and 200 mg.kg(-1). In contrast, GT showed higher TBARS values at 200 mg.kg(-1). Administration of combinations of TC, RO, and GT did not reveal synergistic effects but confirmed the increase in TBARS values with increasing doses of GT. No differences (P > 0.05) among the different antioxidant treatments were detected for protein oxidation. The muscle alpha-tocopherol content linearly responded to the feed alpha-tocopherol content and thus there were no indications for a sparing effect on alpha-tocopherol from other antioxidant treatments. In summary, dietary natural antioxidant extracts were less effective than the treatment with synthetic antioxidants combined with alpha-tocopheryl acetate for protecting against oxidation, but there were marked differences between different natural antioxidant extracts.

Effect of dietary antioxidant and fatty acid supply on the oxidative stability of fresh and cooked pork

The effect of dietary oil (linseed or soybean oil) and antioxidant treatment (α-tocopheryl acetate (AT; 40ppm) versus a cocktail (AOC; 200ppm): α-tocopheryl acetate+rosemary+citric acid+gallic acid) on colour, lipid and protein oxidation of fresh and processed pork was investigated. No effect of oil source on different parameters of oxidation was seen. No effect of antioxidant treatment on colour stability of fresh longissimus thoracis (LT) or cooked cured ham (CCH) was observed. For both antioxidant treatments, lipid oxidation in fresh LT and CCH was well controlled during display. However, lipid oxidation increased significantly in pre-frozen uncured cooked meat under aerobic conditions. No unambiguous effect of antioxidant treatment on protein oxidation was observed. There seemed to be no clear link between colour, protein and lipid oxidation. At the dose used in this study, no additional or synergistic effects of the extra components of the AOC on the different oxidation parameters was found.

Effect of dietary antioxidant supplementation on the oxidative status of plasma in broilers

In this study, the effect of dietary antioxidants on the plasma oxidative status of growing birds fed a diet rich in polyunsaturated fatty acids was investigated. One-day-old broilers were fed for 42 days a diet containing 4% linseed oil and supplemented with single plant extracts rich in antioxidants (natural tocopherols, rosemary, grape seed, green tea, tomato) or a combination of some of these plant extracts, in two different total doses (100 and 200 mg product/kg feed). A diet with synthetic antioxidants with and without α-tocopheryl acetate (200 mg/kg feed) were also included. The plasma oxidative status was evaluated measuring the ferric reducing ability of plasma (FRAP), the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity. Lipid peroxidation was measured by thiobarbituric acid-reactive substances (TBARS). No significant effect of the dietary treatments was observed for FRAP as well as for TBARS. However, diet affected GSH-Px activity (p = 0.002) and a trend for an effect on SOD activity was observed (p=0.084). A higher GSH-Px activity was found for 200 mg/kg tomato extract and natural α-tocopherol in relation to the corresponding 100 mg/kg treatment, and the lowest GSH-Px activity was measured for the synthetic antioxidants treatment. The lowest and highest SOD activity were found for the 200. and 100 mg/kg treatment with tomato extract respectively. In conclusion, the oxidative status and lipid oxidation of plasma in broilers was not affected by feeding natural antioxidant extracts at the doses in the present study, but some changes in antioxidant enzyme activities were observed, of which the implication remains to be elucidated.

Crystallization behavior of milk fat obtained from linseed-fed cows

Milk with an increased content of unsaturated fatty acids was obtained by incorporating 60% of extruded linseed into the concentrate of cows. Two groups of Holstein cows (3 animals/group) were fed a concentrate (control or linseed enriched) together with the same roughage diet (ad libitum). After an adaptation period of 3 wk, evening and morning milk samples were collected every 7 d for 3 wk. Milk was decreamed and anhydrous milk fat (AMF) was isolated from the fat fraction by using the Bureau of Dairy Industries method. The objective of this study was to investigate if the crystallization mechanism of milk fat changed when the content of unsaturated fatty acids was increased. Therefore, the crystallization behavior of a milk fat enriched with unsaturated fatty acids was compared with that of a control milk fat. Nonisothermal crystallization was investigated with differential scanning calorimetry, and 1-step and 2-step isothermal crystallization behaviors were investigated using pulsed nuclear magnetic resonance, differential scanning calorimetry, and x-ray diffraction. A higher content of unsaturated fatty acids in AMF resulted in an increased proportion of low melting triglycerides. These triglycerides lowered the solid fat content profile, particularly at refrigerator temperatures. Furthermore, they induced some changes in the crystallization and melting behaviors of milk fat compared with a control AMF, although no fundamental changes in the crystallization mechanism could be revealed. Even though a lower melting point could be observed for milk fat with a higher content of unsaturated fatty acids, a similar degree of supercooling was needed to initiate crystallization, resulting in a shift in onset temperature of crystallization toward lower temperatures. In addition, slower crystallization kinetics were measured, such as a lower nucleation rate and longer induction times, although crystallization occurred in a similar polymorphic crystal lattice. During melting, a shift in offset temperature toward lower temperatures could be observed for the 3 melting fractions of AMF in addition to a higher proportion of low melting triglycerides. These results demonstrate that a higher content of unsaturated fatty acids has some effect on the crystallization behavior of milk fat. This knowledge could be used to produce dairy products of similar or superior quality compared with conventional products by intervening in the production process of dairy products.

Understanding and preventing consumer milk microbial spoilage and chemical deterioration.

Abstract: This chapter gives a broad overview of the possible spoilage defects in consumer milk, being either of a microbiological nature (e.g. spore formers and Pseudomonas enzymes) or of a chemical nature (e.g. light-induced oxidation). As these defects can be quite specific for, e.g., pasteurised versus ultra high temperature (UHT) treated milk, a detailed description of the mechanisms of spoilage, the main factors (on farm or industry level) influencing this spoilage, and the methods (including emerging methods on farm or industry level) to prevent spoilage, are discussed for different types of consumer milk. Finally, some future trends and further reading advice are given.