F.R. van de Voort

Textural and Microstructural Changes in Corn Starch as a Function of Extrusion Variables

Abstract The effect of extrusion variables (temperature, feed moisture and screw speed) on the expansion, breaking strength and microstructure of starch extrudates was studied using response surface methodology. For expansion the most significant variable was found to be feed moisture which bore an inverse relation to the expansion response. All the extrusion variables studied were significantly related to expansion and accounted for 95.7% of the total variation. Screw speed and feed moisture were the most significant variables for breaking strength, all three variables accounting for 89.7% of the total break strength variation. Microstructure of the extrudates could be related to the extrusion variables, the expansion and breaking strength responses. The porosity of the extrudates increased with decreasing moisture, with a concomitant increase in expansion and a decrease in breaking strength. Regression equations generated from composite rotatable response surface design experiments could be used to accurately predict the responses studied.

An HPLC method for simultaneous quantitation of individual isothiocyanates and oxazolidinethione in myrosinase digests of rapeseed meal

A simple, rapid and precise method for simultaneous quantitation of individual isothiocyanates and oxazolidinethione inmyrosinase digests of rapeseed meal has been developed. The method consists of inactivation of native myrosinase activity present in the seedmeal, followed by digestion with mustard myrosinase (thioglucoside glucohydrolase, EC 3.2.3.1) to hydrolyze rapeseed glucosinolates quantitatively to isothiocyanates and oxazolidinethione. These hydrolytic products are extracted in methylene chloride as soon as they are formed and finally resolved by a reverse phase high pressure liquid chromatography (HPLC) technique on a μ Bondapak C18 column using aqueous acetonitrile as solvent and an ultraviolet (UV) absorbance detector set at 254 nm. The lower limits of quantitation by this method in a single aliquot applied to the column were 0.2 μg for the isothiocyanates and 0.01 μg for the oxazolidinethione. Recoveries of allyl isothiocyanate, oxazolidinethione and sinigrin added toB. juncea, prior to digestion, were quantitative and averaged at 94.5, 93.0 and 91.2 percent with standard deviations of 1.5, 3.3 and 2.8 percent, respectively. The butenyl and pentenyl isothiocyanates and oxazolidinethione in Tower (B. napus) and Candle (B. campestris) rapeseeds, and allyl isothiocyanate inB. juncea were the major hydrolytic products of glucosinolates. The identity of peaks corresponding to these compounds on a HPLC chromatogram was confirmed by mass spectroscopy.

Microwave treatment of dehulled rapeseed to inactivate myrosinase and its effect on oil and meal quality

Rapeseed was dehulled using a Palyi pneumatic attrition system which produced 62–66% clean dehulled seed. Dehulled rapeseed was preconditioned to 7, 10 and 13% moisture levels, exposed to micro-wave irradiation for periods of up to 2.5 min and analyzed for residual thioglucoside glucohydrolase (myrosinase) activity. The 7% moisture samples heated slowly and required at least a 2.5 min treatment whereas 10 and 13% moisture samples heated more rapidly and required microwave exposures of 1.5 min or less for complete inactivation of the enzyme. The sulfur content of oils obtained from adequately microwave-treated samples (1.5 min for 10 and 13% and 2.5 min for 7% moisture samples) was equal to or lower than commercially processed crude rapeseed oils. The shorter microwave treatment of dehulled rapeseed produced considerably lighter oils and did not adversely affect the color of the meal. It also destroyed some of the rapeseed glucosinolates and improved the meal palatability. However, goitrogenic properties of microwave-treated rapeseed meal evaluated by mice feeding experiments did not appear different from untreated rapeseed meal.

The Heat Stability of Allyl Glucosinolate (Sinigrin) in Aqueous and Model Systems

Abstract The thermal decomposition of allyl glucosinolate (sinigrin) by conventional and microwave heating was studied in aqueous and model systems. Decomposition of sinigrin by conventional heating in the aqueous system (phosphate buffer, pH 5.9, ionic strength, 0.2) was found to be a first order reaction with activation energy of 94.5 KJ/mole (22.6 Kcals/mole). Microwave irradiation of aqueous system samples for short periods of 0.5xa0min or more also resulted in decomposition of this glucosinolate. Decomposition of sinigrin by microwave heating in a model system formulated using soya and pure sinigrin monohydrate was found to be a function of the adjusted initial moisture level and the exposure period. Among the 7–20% moisture samples, the minimum decomposition occurred in 7% moisture samples which appeared to be due to relatively slow heating of these samples on exposure to microwave irradiation. More sinigrin was decomposed in the soya model system with increasing periods of microwave irradiation. Although a 3xa0min microwave exposure of soya model system samples resulted in scorching, it did not cause complete decomposition of sinigrin.

The quantitative analysis of fat and protein in meat by transmission infrared analysis

Transmission infrared analysis, which has been successfully applied to milk analysis, was assessed for the quantitative analysis of fat and protein in meat products. Meats of varying fat and protein content were converted into milk-like emulsions, which were, in turn, analyzed by standard chemical methods and by a Multispec M infrared analyzer. The performance of the instrument for meat analysis using a standard milk calibration was also assessed and compared with the instrument set with a meat calibration. Both approaches provided a good estimate of the fat and protein content for a range of meat products, the meat calibration being more accurate than the milk calibration. The infrared method allowed for rapid and accurate analysis of meat and has future potential in the meat industry for quality control purposes.

Determination of solid fat index of fats and oils using the anton paar density meter

The Anton Paar Density Meter was investigated for its potential use in the determination of Solid Fat Index (SFI) of fats and oils. By deriving equations for the behavior of instrument constants as a function of temperature, the specific volume of a fat could be determined as it underwent heating at a controlled rate of 2 C/min. The specific volume data obtained as a function of temperature could be converted into SFI data by minor modifications to the AOCS dilatometry equations, and hence provide a smooth SFI curve for fats and oils. The method was capable of providing more detailed dilation data in a shorter period of time and the SFI values determined related well to the conventional dilatometric technique.

Comparison of the direct and indirect wide-line nuclear magnetic resonance methods for determining solid fat content

A direct method of measuring the solid fat content by wide-line nuclear magnetic resonance (NMR) was compared with the conventional indirect wide-line NMR procedure. The direct method is based on the use of variable gate widths available on the Newport Analyser Mk IIIA. The results obtained for four different fats using the direct method did not differ significantly from those of the indirect method. As the direct method required additional measurements, was somewhat more complex theoretically and gave more variable results because of the weaker signal obtained at the wide gate, no real advantage could be found for its use.

Effect of Extrusion Variables on Product Moisture and Extrusion Crystallinity of Corn Starch

Abstract The effect of primary extrusion variables, temperature, feed moisture and screw speed on product moisture and extrusion crystallinity in corn starch was studied using response surface methodology. Both extrusion crystallinity and product moisture were related to the primary variables accounting for 84.47% and 90.66% (P

Automated reading and recording of sensory data for semi-structured scales

Abstract The use of Optical Mark Reader (OMR) cards is proposed, explained and tested as a potential substitute for the conventional semi-structured scale used in sensory evaluation. The use of OMR cards allows the direct transfer of data from the panelist to the computer, bypassing the tedious measuring, recording and data entry steps normally required. Statistical assessment of the OMR method in relation to the semi-structured approach indicates that comparable results can be obtained.