I N T R O D U C T I O N . . 142 IN VIVO D I G E S T I O N I N SIMPLE-STOMACH A N I M A L S . . 142 S T O M A C H . . . 143 SMALL INTESTINE . . 143 H I N D G U T . . 143 FACTORS I N F L U E N C I N G DIGESTIBILITY I N V I V O . . 144 I N VITRO M E T H O D S FOR E S T I M A T I N G D I G E S T I B I L I T Y . . . 145 D I A L Y S I S CELL METHOD . . 145 Objective . . 145 Principle . . 145 Methods. . . 145 Results . . 145 Discussion . . 146 PH-DROP A N D PH-STAT M E T H O D . . . 146 Objective . . 146 Principle . . 146 Methods. . . 146 Results . . . 146 Discussion . . 147 COLORIMETRIC METHODS . . 147 Objective . . 147 Principle . . 147 Methods. . . 147 Results . . . 148 Discussion . . 148 ‘ F I L T R A T I O N ’ M E T H O D S . . 148 Objective . . 148 Principle . . 148

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Critical Evaluation of in Vitro Methods for Estimating Digestibility in Simple-Stomach Animals

Milk products are especially sensitive to the effects of heat treatment encountered under conventional process and storage conditions because of an abundance of reactive functional groups: aldehyde group of lactose, e-amino group of lysine and other reactive N-containing groups (e.g. indolyl group of tryptophan, imidazole group of histidine, guanidino group of arginine and the α-amino group of proteins and free amino acids).

Non-Enzymatic Degradation Pathways of Lactose and Their Significance in Dairy Products

Milk products are especially sensitive to the effects of heat treatment encountered under conventional process and storage conditions because of an abundance of reactive functional groups: aldehyde group of lactose, e-amino group of lysine and other reactive N-groups (e.g. indolyl group of tryptophan, imidazole group of histidine, guanidino group of arginine and the α-amino group of proteins and free amino acids).

Reaction Chemistry of Lactose: Non-Enzymatic Degradation Pathways and Their Significance in Dairy Products

An optical biosensor for lysine based on the use of lysine decarboxylase and a cadaverine-sensitive membrane.

Summary The use of spectrophotometric methods to monitor Maillard browning reactions has been described by many authors. The limitation of such methods is lack of specificity. The present work describes a new approach using an enzyme electrode (immobilized α-L-Lysine oxidase from Trichoderma viride) to evaluate lysine loss. The experiments were conducted at 120°C (30 minutes, pH 5) with the lysine-glucose molar ratio varying from 0.2 to 1.0. Lysine loss was highly correlated with spectrophotometric data (A287 nm) using least squares polynomial fitting (R2=0.991). The data obtained the microwave spectral analysis (scanning between 2400 and 2450 MHz) were also highly correlated with lysine loss (R2=1). This technique is based on dielectric properties of the media to be analyzed. It was able to show the importance of the polar groups that were formed (amplitude of the spectrum) and the structure change (frequency of the spectrum) with the Maillard model system. The experiment was extended to different carbohydrates (pentoses and hexoses) at a fixed molar ratio. The results agreed with those in the literature: lysine loss was higher with pentoses.

Evaluation of a Lysine-Glucose Maillard Model System Using Three Rapid Analytical Methods

As an alternative to the classic ion-exchange chromatography for lysine determination, a new specific enzymatic method based on the use of lysine oxidase was developed. Results obtained on Maillard model reactions and on samples from soybeam meal hydrolysates are described. The levulinic acid formed from acid degradation of glucose was shown to negatively affect lysine determination. Different hydrolysis conditions were examined for soybean meal

Dc. Bruyer

Papers

Use of a lysine oxidase electrode for lysine determination in Maillard model reactions and in soybean meal hydrolysates