Pro- and antioxidative activity of protein fractions from pork (longissimus dorsi)

Protein fractions from pork (longissimus dorsi), isolated in search of the factor in meat enhancing non-heme iron absorption, have been analysed for their effect on radical formation and oxidation processes. In heat-treated minced meat samples with the protein fractions incorporated, the water-soluble proteins showed a prooxidative effect on lipid oxidation compared to the salt-soluble and the insoluble proteins, which did not influence oxidation in the meat system relative to control samples. The level of secondary oxidation products in meat samples with water-soluble proteins added was, however, not as high as would be expected from the ability of this protein fraction to initiate oxidation as measured by spin-trapping ESR-spectroscopy in meat emulsions and by oxygen depletion rates in a lipid model system with the protein fraction added. In agreement with this observation, the water-soluble protein fraction was found, in addition to being prooxidative, also to have the highest antioxidative potential of the three protein fractions as measured by spin probing ESR-spectroscopy (Fremy's salt method). The prooxidative activity of the water-soluble proteins was assigned to myoglobin and hemoglobin derivatives (detected spectrophotometrically), emphasising the role of iron-catalysis in oxidative deterioration of meat products.     

Distribution of Penicillium commune isolates in cheese dairies mapped using secondary metabolite profiles, morphotypes, RAPD and AFLP fingerprinting

In an 8-year study of the diversity and distribution of Penicillium commune contaminants in two different cheese dairies, swab and air samples were taken from the production plants, the processing environment and contaminated cheeses. A total of 321 Penicillium commune isolates were characterized using morphotypes (colony morphology and colours) and secondary metabolite profiles. Based on production of secondary metabolites the P. commune isolates were classified into 6 groups. The genetic diversity of the P. commune isolates was assessed using randomly amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). For a sub-set of 272 P. commune isolates RAPD analysis generated 33 RAPD groups whereas AFLP profiling revealed 55 AFLP groups. This study conclusively showed that the discriminatory power of AFLP was high compared to RAPD and that AFLP fingerprinting matched morphotyping. P. commune isolates with identical profiles using all four typing techniques were interpreted as closely related isolates with a common origin and the distribution of these isolates in the processing environment indicated possible contamination points in the cheese dairies. The coating process and unpacking of cheeses with growth of P. commune seemed to cause the contamination problems. Several identical P. commune isolates remained present in the processing environment for more than 7 years in both dairies.     

Total Synthesis of desB30 Insulin Analogues by Biomimetic Folding of Single‐Chain Precursors

Insulin is a peptide hormone consisting of 51 amino acids in two chains with three disulfide bridges. Human insulin and various analogues are used for the treatment of diabetes and are produced recombinantly at ton scale. Herein, we report the chemical synthesis of insulin by the step‐wise, Fmoc‐based, solid‐phase synthesis of single‐chain precursors with solubilising extensions, which under redox conditions, spontaneously fold with the correct pairing of the three disulfide bridges. The folded, single‐chain, insulin precursors can be transformed into bioactive two‐chain desB30 insulin by the simultaneous removal of the solubilising extension (4–5 residues) and the chain‐bridging C‐peptide (3–5 residues) by employing Achromobacter lyticus protease—a process well‐known from the yeast‐based recombinant production of insulin. The overall yields of synthetic insulins were as much as 6 %, and the synthetic process was straightforward and not labour intensive.     

Content of some organic acids in cloudberry (Rubus chamaemorus L.)

Cloudberry (Rubus chamaemorus L.) is very resistant to deterioration by micro-organisms and has a good keeping quality. In the present study the natural content of some organic acids, often used as food preservatives, has been determined by gas chromatography. Benzoic acid was found in the greatest amount (about 50 mg/100 g cloudberry). Sorbic acid, salicylic acid, ?-hydroxy-, methyl-?-hydroxy-and propyl-?-hydroxy-benzoic acid were found in smaller amounts (less than 1 mg/100 g cloudberry).The amount of benzoic acid changes very little with the degree of ripeness or place of growth.     

Heat inactivation and pH optima of peroxidase and catalase in carrot,swede and Brussels sprouts

Heat inactivation and pH optima of the enzymes peroxidase and catalase were studied in carrot, swede and Brussels sprouts. There were differences in the heat stabilities of the peroxidases from different vegetables, but all peroxidases were more heat stable than the catalases. From the pH profiles and the heat stability curves it was concluded that both the peroxidases and catalases in the three vegetable species are somewhat different. Lipoxygenase and phenolase activities were not detected by the methods used.     

Oxidative changes in pork scratchings,peanuts, oatmeal and muesli viewed by fluorescence,near-infrared and infrared spectroscopy

The possibility of using rapid spectroscopic methods to detect lipid oxidation of four standard food products—peanuts, pork scratchings, oatmeal and muesli—were investigated in a large screening experiment. Fluorescence, near-infrared [including visual (Vis/NIR)] and infrared (IR) spectra have been recorded during and beyond the normal shelf lives of the products and related by means of multivariate data analysis to reference oxidation measures of free radicals and hexanal, as well as to sensory evaluation. For pork scratchings, the three spectroscopic techniques were able to monitor the progressing level of oxidation: IR with good correlation to hexanal (r²=0.86), Vis/NIR with good correlations to free radicals (r²=0.82) and fluorescence with good correlations to both free radicals (r²=0.76) and hexanal (r²=0.83). In the case of IR, the best result was obtained using the region including the out-of-plane C–H of trans-fatty acids. For the other three products, the results were generally inferior except for good correlations between fluorescence spectra and free radicals in peanuts (r²=0.73) and between Vis/NIR spectra and hexanal for muesli products (r²=0.8).     

Can spectroscopy in combination with chemometrics replace minks in digestibility tests?

One of the most relevant but expensive methods of assessing the quality of fish meal is the physiological digestibility test with minks. The purpose of this study was to determine whether spectroscopic and chemical analyses evaluated with chemometrics can replace minks in digestibility tests. The spectroscopic methods used were the two complementary techniques of fluorescence emission and near‐infrared reflectance. The investigation included 54 samples of high‐quality fish meal ranging from 89.6 to 93.9 on the mink digestibility index. The investigation also included determination of seven quality parameters in the fish meal to substantiate the spectroscopic models on the mink digestibility. These quality parameters include the content of protein, oil, water, water‐soluble protein, ash and the biogenic substance cadaverine as well as the titration value. The study demonstrates that the mink digestibility could be predicted from combining the two reference quality parameters oil and ash with a correlation coefficient of 0.89. The best spectroscopic calibration models on the mink digestibility resulted in a correlation coefficient of 0.94 and a prediction error of 0.5 using the near‐infrared spectral ensemble and a correlation coefficient of 0.92 and a prediction error of 0.5 using the fluorescence spectral ensemble. In addition, the seven reference quality parameters could be predicted from the spectroscopic ensembles with good precision. © 2000 Society of Chemical Industry     

Effects of Emulsifiers on Protein-Fat Interaction in Ice Cream Mix during Ageing I: Quantitative Analyses

Ageing of ice cream mix at 0 to 10°C for a minimum of 3 up to 24 hours prior to ice cream production in the ice cream machine is generally used to improve various physical properties. During ageing the fat phase of the mix crystallizes and protein is slowly desorbed from the surface of the fat globules. In the presence of emulsifiers fat crystallization and protein desorption is distinctly enhanced resulting in increased agglomeration of fat globules during ice cream manufacture which is important for the formation and stability of the final ice cream. The effect of emulsifiers on ageing is due to their strong interfacial activity at low temperature.