No abstract

Partial replacement of animal protein sources with plant proteins is highly relevant for the food industry, but potential effects on protein digestibility need to be established. In this study, the in vitro protein digestibility (IVPD) of four protein sources and their mixtures (50:50 w/w ratio) was investigated using a transient pepsin hydrolysis (1 h) followed by pancreatin (1 h). The protein sources consisted of napin-rich rapeseed (Brassica napus L.) protein concentrates (RPCs; RP1, RP2) prepared in pilot scale and major bovine whey proteins (WPs; α-LA, alpha-lactalbumin; β-LG, beta-lactoglobulin). IVPD of individual protein sources was higher for WPs compared to RPCs. The RP2/β-LG mixture resulted in an unexpected high IVPD equivalent to β-LG protein alone. Protein mixtures containing RP1 showed a new IVPD response type due to the negative influence of a high trypsin inhibitor activity (TIA) level. Improved IVPD of RP1 alone and in protein mixtures was obtained by lowering the TIA level using dithiothreitol (DTT). These results showed that napin-rich protein products prepared by appropriate processing can be combined with specific WPs in mixtures to improve the IVPD.

longed shelf-life by inactivation of micro-organisms and enzymes. HP/HT can at temperatures above 50 o C lead to pasteurization using pressure levels from 250-500 MPa [Wilson et al., 2008], while sterilization can be obtained with HP at temperatures higher than 70 o C . Focus is thus on the application of HP in combination with high temperatures (HT), which may lead to tissue compression, cell wall breakage and cell membrane disruption, depending on the HP and HT levels as well as the type of vegetable or fruit that are treated [Michel & Autio, 2002]. In the present study, where broccoli has been processed, the food quality is particularly connected with the enzyme-substrate (myrosinase--glucosinolate) system, where the different types of non-enzymatic and enzymatic catalyzed hydrolysis products give rise to effects from being health promoting to affecting the taste and odor [Hansen et al., 1995[Hansen et al., , 1997 Jeffery & Aray, 2009].PEF is considered a non-thermal treatment, which can lead to pasteurization at ambient temperatures using electrical field strengths of 20-30 kV/cm, and short pulses of 1-10 µs [Mosqueda-Melgar et al., 2008]. Application of short electric pulses may result in pore formation in cell membranes, and depending on the treatment intensity, time, electric field and pulse energy the membrane permeabilisation High pressure/high temperature (HP/HT) and pulsed electric field (PEF) treatment of food are among the novel processing techniques considered as alternatives to conventional thermal food processing. Introduction of new processing techniques with fast and gentle processing steps may reveal new possibilities for preservation of healthy bioactive compounds in processed food. However, effects on various food components due to autolysis and fast reactions prior to the applied HP/HT or PEF need to be considered as the total contribution of processing steps affects the obtained food quality. The present experiments were performed on broccoli (Brassica oleracea var. Italica) florets, purée and juice. Specific focus was given to effects of HP/HT and PEF processing on the content of glucosinolates and activities of myrosinase isoenzymes (EC.3.2.1.147) in the broccoli preparations. Certain conditions applied in HP/HT processing of broccoli florets were able to maintain a high level of intact glucosinolates. Treatment at 700 MPa and 20°C for 10 min was found to inactivate myrosinase activity, but also pressure treatments at 300 MPa and 20°C were able to maintain a high level of intact glucosinolates present in the untreated broccoli florets. PEF processing of broccoli purée and juice showed that the myrosinase activities resulted in nearly total glucosinolate transformations as result of autolysis during puréeing and juice making prior to the PEF processing. These data demonstrated that insight into potential effects on myrosinase activities from application of PEF processing implies specific focus on the sample steps preceding the PEF processing. Processing of broccoli and autolysis reaction...

BV, biological value; DF, dietary fi bre; DH, degree of hydrolysis; DM, dry matter; E:S ratio, enzyme to substrate ratio; IDF, insoluble dietary fi bre; IVPD, in vitro protein digestibility; IVPD PT, overall protein digestibility; NSP, non-starch polysaccharides; PD, protein digestibility; RE, rapeseed embryo fi bres; RH, rapeseed hulls; RP(2), rapeseed protein concentrate (2) rich in napin proteins; SDF, soluble dietary fi bre; TD, true protein digestibility; TDF, total dietary fi bre; TDF-RE, total dietary fi bre isolated from rapeseed embryo fi bres; TDF-RH, total dietary fi bre isolated from rapeseed hulls; TNBS, trinitrobenzenesulfonic acid; U-samples, untreated samples; UPT-samples, uncorrected overall protein digestibility samples.

No abstract