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Papers by kees van kekem

Research paper thumbnail of Effects of sucrose on salivary flow and composition: differences between real and sham intake

International Journal of Food Sciences and Nutrition, Nov 18, 2009

Human saliva contains numerous salivary components that are fundamental for a healthy oral enviro... more Human saliva contains numerous salivary components that are fundamental for a healthy oral environment and the oral processing of foods. To study a possible differential influence of orosensory stimulation and metabolic activation on salivary composition, human parotid salivary flow, pH, A 280 , and a-amylase activity were measured before, during and after real or sham (sipand-spit) sucrose intakes. Variations in these salivary characteristics were related to perceived satiety. Sucrose, as either real or sham intake, increased salivary flow and pH and decreased A 280 before returning to pre-intake levels. Increased salivation was dependent on the sucrose concentration and was accompanied with a higher pH and lower A 280. After sucrose ingestion, the salivary a-amylase activity increased, while no increase occurred after sham sucrose intake. Similarly, rated satiety increased with real but not by sham sucrose intake. This indicated that salivary a-amylase is associated with perceived satiety controlled by caloric perception downstream of the oral cavity.

Research paper thumbnail of Optimized enzymatic synthesis of C-terminal peptide amides using subtilisin A from Bacillus licheniformis

Journal of Molecular Catalysis B-enzymatic, Sep 1, 2010

A mild and efficient method for the conversion of C-terminal esters of side-chain protected pepti... more A mild and efficient method for the conversion of C-terminal esters of side-chain protected peptides into an amide function via enzyme-catalysed ammonolysis in organic media with low water content is described. Subtilisin A, the alkaline serine protease from Bacillus licheniformis, was used as biocatalyst and ammonium carbamate as source of ammonia. Response surface methodology (RSM) and central composite design were

Research paper thumbnail of Effect of Pasteurization by Moderate Intensity Pulsed Electric Fields (PEF) Treatment Compared to Thermal Treatment on Quality Attributes of Fresh Orange Juice

Foods, Oct 25, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Proteins from plant-based biomass: effects of post-harvest conditions on protein retention and quality : Part II Yellow pea

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system ... more All rights reserved. No part of this publication may be reproduced, stored in a retrieval system of any nature, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. The publisher does not accept any liability for inaccuracies in this report. Confidential until 12-2022 Wageningen Food & Biobased Research-Report 2174 | 3 Contents Summary 1 Introduction 2 Materials and Methods 2.1 General setup 2.2 Plant material 2.3 Storage conditions and storage period 2.4 Analysis 2.4.1 Initial measurements starting material 2.4.2 Pea weight ('fresh weight') 2.4.3 Dry matter 2.4.4 Colour 2.4.5 Proteins 2.4.5.1 Sample preparation for protein extraction 2.4.5.2 Protein extractions 2.4.5.3 Protein content (BCA assay) 2.4.5.4 Protein composition (SDS-PAGE) 2.4.5.5 Glycation 2.4.6 Hexanal (marker for volatile off-flavour) 2.4.7 Saponins 3 Results 3.1 Pea weight 3.2 Moisture content 3.3 Colour 3.4 Protein content (BCA assay) 3.5 Protein composition (SDS-page) 3.6 Glycation 3.6.1 Glycation 1 st experiment 3.6.2 Glycation 2 nd experiment 3.6.3 Glycation 3 rd experiment 3.6.4 Glycation 4 th experiment: Differential Scanning Calorimetry (DSC)

Research paper thumbnail of Proteins from plant-based biomass: effects of post-harvest conditions on protein retention and quality : Part II Yellow pea

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system ... more All rights reserved. No part of this publication may be reproduced, stored in a retrieval system of any nature, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. The publisher does not accept any liability for inaccuracies in this report. Confidential until 12-2022 Wageningen Food & Biobased Research-Report 2174 | 3 Contents Summary 1 Introduction 2 Materials and Methods 2.1 General setup 2.2 Plant material 2.3 Storage conditions and storage period 2.4 Analysis 2.4.1 Initial measurements starting material 2.4.2 Pea weight ('fresh weight') 2.4.3 Dry matter 2.4.4 Colour 2.4.5 Proteins 2.4.5.1 Sample preparation for protein extraction 2.4.5.2 Protein extractions 2.4.5.3 Protein content (BCA assay) 2.4.5.4 Protein composition (SDS-PAGE) 2.4.5.5 Glycation 2.4.6 Hexanal (marker for volatile off-flavour) 2.4.7 Saponins 3 Results 3.1 Pea weight 3.2 Moisture content 3.3 Colour 3.4 Protein content (BCA assay) 3.5 Protein composition (SDS-page) 3.6 Glycation 3.6.1 Glycation 1 st experiment 3.6.2 Glycation 2 nd experiment 3.6.3 Glycation 3 rd experiment 3.6.4 Glycation 4 th experiment: Differential Scanning Calorimetry (DSC)

Research paper thumbnail of Effect of Pasteurization by Moderate Intensity Pulsed Electric Fields (PEF) Treatment Compared to Thermal Treatment on Quality Attributes of Fresh Orange Juice

Foods

Novel pulsed electric field (PEF) process conditions at moderate electric field strength and long... more Novel pulsed electric field (PEF) process conditions at moderate electric field strength and long pulse duration have recently been established to obtain microbial inactivation. In this study, the effect of these PEF conditions (E = 0.9 and 2.7 kV/cm, with pulse duration 1000 µs) at variable maximum temperatures was evaluated on quality attributes of freshly squeezed orange juice. Results were compared to orange juice that received no treatment or a mild or severe thermal pasteurization treatment. No differences for pH and soluble solids were found after application of any treatment, and only small differences were observed for color and vitamin C content (ascorbic acid and dehydroascorbic acid) after processing, mainly for conditions applied at higher temperature. Variations in the maximum temperatures of the PEF and thermal processes led to differences in flavor compounds and the remaining activity of pectinmethylesterase (PME). At PEF conditions with a maximum temperature of 78 °...

Research paper thumbnail of A simple, sensitive, and specific method for the extraction and determination of thiamine and thiamine phosphate esters in fresh yeast biomass

Journal of Microbiological Methods

Research paper thumbnail of Optimized enzymatic synthesis of C-terminal peptide amides using subtilisin A from Bacillus licheniformis

Journal of Molecular Catalysis B: Enzymatic, 2010

A mild and efficient method for the conversion of C-terminal esters of side-chain protected pepti... more A mild and efficient method for the conversion of C-terminal esters of side-chain protected peptides into an amide function via enzyme-catalysed ammonolysis in organic media with low water content is described. Subtilisin A, the alkaline serine protease from Bacillus licheniformis, was used as biocatalyst and ammonium carbamate as source of ammonia. Response surface methodology (RSM) and central composite design were

Research paper thumbnail of Effects of sucrose on salivary flow and composition: differences between real and sham intake

International Journal of Food Sciences and Nutrition, 2009

Human saliva contains numerous salivary components that are fundamental for a healthy oral enviro... more Human saliva contains numerous salivary components that are fundamental for a healthy oral environment and the oral processing of foods. To study a possible differential influence of orosensory stimulation and metabolic activation on salivary composition, human parotid salivary flow, pH, A(280), and alpha-amylase activity were measured before, during and after real or sham (sip-and-spit) sucrose intakes. Variations in these salivary characteristics were related to perceived satiety. Sucrose, as either real or sham intake, increased salivary flow and pH and decreased A(280) before returning to pre-intake levels. Increased salivation was dependent on the sucrose concentration and was accompanied with a higher pH and lower A(280). After sucrose ingestion, the salivary alpha-amylase activity increased, while no increase occurred after sham sucrose intake. Similarly, rated satiety increased with real but not by sham sucrose intake. This indicated that salivary alpha-amylase is associated with perceived satiety controlled by caloric perception downstream of the oral cavity.

Research paper thumbnail of Effects of sucrose on salivary flow and composition: differences between real and sham intake

International Journal of Food Sciences and Nutrition, Nov 18, 2009

Human saliva contains numerous salivary components that are fundamental for a healthy oral enviro... more Human saliva contains numerous salivary components that are fundamental for a healthy oral environment and the oral processing of foods. To study a possible differential influence of orosensory stimulation and metabolic activation on salivary composition, human parotid salivary flow, pH, A 280 , and a-amylase activity were measured before, during and after real or sham (sipand-spit) sucrose intakes. Variations in these salivary characteristics were related to perceived satiety. Sucrose, as either real or sham intake, increased salivary flow and pH and decreased A 280 before returning to pre-intake levels. Increased salivation was dependent on the sucrose concentration and was accompanied with a higher pH and lower A 280. After sucrose ingestion, the salivary a-amylase activity increased, while no increase occurred after sham sucrose intake. Similarly, rated satiety increased with real but not by sham sucrose intake. This indicated that salivary a-amylase is associated with perceived satiety controlled by caloric perception downstream of the oral cavity.

Research paper thumbnail of Optimized enzymatic synthesis of C-terminal peptide amides using subtilisin A from Bacillus licheniformis

Journal of Molecular Catalysis B-enzymatic, Sep 1, 2010

A mild and efficient method for the conversion of C-terminal esters of side-chain protected pepti... more A mild and efficient method for the conversion of C-terminal esters of side-chain protected peptides into an amide function via enzyme-catalysed ammonolysis in organic media with low water content is described. Subtilisin A, the alkaline serine protease from Bacillus licheniformis, was used as biocatalyst and ammonium carbamate as source of ammonia. Response surface methodology (RSM) and central composite design were

Research paper thumbnail of Effect of Pasteurization by Moderate Intensity Pulsed Electric Fields (PEF) Treatment Compared to Thermal Treatment on Quality Attributes of Fresh Orange Juice

Foods, Oct 25, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Proteins from plant-based biomass: effects of post-harvest conditions on protein retention and quality : Part II Yellow pea

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system ... more All rights reserved. No part of this publication may be reproduced, stored in a retrieval system of any nature, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. The publisher does not accept any liability for inaccuracies in this report. Confidential until 12-2022 Wageningen Food & Biobased Research-Report 2174 | 3 Contents Summary 1 Introduction 2 Materials and Methods 2.1 General setup 2.2 Plant material 2.3 Storage conditions and storage period 2.4 Analysis 2.4.1 Initial measurements starting material 2.4.2 Pea weight ('fresh weight') 2.4.3 Dry matter 2.4.4 Colour 2.4.5 Proteins 2.4.5.1 Sample preparation for protein extraction 2.4.5.2 Protein extractions 2.4.5.3 Protein content (BCA assay) 2.4.5.4 Protein composition (SDS-PAGE) 2.4.5.5 Glycation 2.4.6 Hexanal (marker for volatile off-flavour) 2.4.7 Saponins 3 Results 3.1 Pea weight 3.2 Moisture content 3.3 Colour 3.4 Protein content (BCA assay) 3.5 Protein composition (SDS-page) 3.6 Glycation 3.6.1 Glycation 1 st experiment 3.6.2 Glycation 2 nd experiment 3.6.3 Glycation 3 rd experiment 3.6.4 Glycation 4 th experiment: Differential Scanning Calorimetry (DSC)

Research paper thumbnail of Proteins from plant-based biomass: effects of post-harvest conditions on protein retention and quality : Part II Yellow pea

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system ... more All rights reserved. No part of this publication may be reproduced, stored in a retrieval system of any nature, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. The publisher does not accept any liability for inaccuracies in this report. Confidential until 12-2022 Wageningen Food & Biobased Research-Report 2174 | 3 Contents Summary 1 Introduction 2 Materials and Methods 2.1 General setup 2.2 Plant material 2.3 Storage conditions and storage period 2.4 Analysis 2.4.1 Initial measurements starting material 2.4.2 Pea weight ('fresh weight') 2.4.3 Dry matter 2.4.4 Colour 2.4.5 Proteins 2.4.5.1 Sample preparation for protein extraction 2.4.5.2 Protein extractions 2.4.5.3 Protein content (BCA assay) 2.4.5.4 Protein composition (SDS-PAGE) 2.4.5.5 Glycation 2.4.6 Hexanal (marker for volatile off-flavour) 2.4.7 Saponins 3 Results 3.1 Pea weight 3.2 Moisture content 3.3 Colour 3.4 Protein content (BCA assay) 3.5 Protein composition (SDS-page) 3.6 Glycation 3.6.1 Glycation 1 st experiment 3.6.2 Glycation 2 nd experiment 3.6.3 Glycation 3 rd experiment 3.6.4 Glycation 4 th experiment: Differential Scanning Calorimetry (DSC)

Research paper thumbnail of Effect of Pasteurization by Moderate Intensity Pulsed Electric Fields (PEF) Treatment Compared to Thermal Treatment on Quality Attributes of Fresh Orange Juice

Foods

Novel pulsed electric field (PEF) process conditions at moderate electric field strength and long... more Novel pulsed electric field (PEF) process conditions at moderate electric field strength and long pulse duration have recently been established to obtain microbial inactivation. In this study, the effect of these PEF conditions (E = 0.9 and 2.7 kV/cm, with pulse duration 1000 µs) at variable maximum temperatures was evaluated on quality attributes of freshly squeezed orange juice. Results were compared to orange juice that received no treatment or a mild or severe thermal pasteurization treatment. No differences for pH and soluble solids were found after application of any treatment, and only small differences were observed for color and vitamin C content (ascorbic acid and dehydroascorbic acid) after processing, mainly for conditions applied at higher temperature. Variations in the maximum temperatures of the PEF and thermal processes led to differences in flavor compounds and the remaining activity of pectinmethylesterase (PME). At PEF conditions with a maximum temperature of 78 °...

Research paper thumbnail of A simple, sensitive, and specific method for the extraction and determination of thiamine and thiamine phosphate esters in fresh yeast biomass

Journal of Microbiological Methods

Research paper thumbnail of Optimized enzymatic synthesis of C-terminal peptide amides using subtilisin A from Bacillus licheniformis

Journal of Molecular Catalysis B: Enzymatic, 2010

A mild and efficient method for the conversion of C-terminal esters of side-chain protected pepti... more A mild and efficient method for the conversion of C-terminal esters of side-chain protected peptides into an amide function via enzyme-catalysed ammonolysis in organic media with low water content is described. Subtilisin A, the alkaline serine protease from Bacillus licheniformis, was used as biocatalyst and ammonium carbamate as source of ammonia. Response surface methodology (RSM) and central composite design were

Research paper thumbnail of Effects of sucrose on salivary flow and composition: differences between real and sham intake

International Journal of Food Sciences and Nutrition, 2009

Human saliva contains numerous salivary components that are fundamental for a healthy oral enviro... more Human saliva contains numerous salivary components that are fundamental for a healthy oral environment and the oral processing of foods. To study a possible differential influence of orosensory stimulation and metabolic activation on salivary composition, human parotid salivary flow, pH, A(280), and alpha-amylase activity were measured before, during and after real or sham (sip-and-spit) sucrose intakes. Variations in these salivary characteristics were related to perceived satiety. Sucrose, as either real or sham intake, increased salivary flow and pH and decreased A(280) before returning to pre-intake levels. Increased salivation was dependent on the sucrose concentration and was accompanied with a higher pH and lower A(280). After sucrose ingestion, the salivary alpha-amylase activity increased, while no increase occurred after sham sucrose intake. Similarly, rated satiety increased with real but not by sham sucrose intake. This indicated that salivary alpha-amylase is associated with perceived satiety controlled by caloric perception downstream of the oral cavity.