Predicting safety and quality parameters for UHT‐processed milks

Abstract

A spreadsheet was developed to evaluate safety and quality parameters for milks subjected to different heating and cooling profiles and holding time conditions in a continuous heat exchanger. Safety parameters evaluated were lethality ( Fo ) and microbial inactivation ( B *) values; quality parameters were chemical change ( C *), thiamin loss, lactulose formation, Maillard browning and hydroxymethylfurfural (HMF) formation. The spreadsheet was used to predict these parameters for a pilot plant, heating milks at 120-150 ° C for 4, 27 and 58 s, using its heating and cooling profiles. Milks were processed in the same plant at these conditions and a selection of the milks were analysed to establish the validity of the spreadsheet. All samples with a C * value < 3 gave a positive Aschaffenburg turbidity. The activation energy that gave the best agreement between the predicted and experimental results for lactulose was found to be 122 kJ/mol. One set of optimized conditions for this product was 135 ° C for 10 s, giving B * = 1.24 and C * = 0.55. This milk was compared with two others and its sensory characteristics were similar to that with a C * of 1.5 but different to that with a C * value of 6. Browning was only found to be noticeable in the most severely heat-treated sample immediately after processing, but would become apparent on storage at 30 ° C and above. The spreadsheet is useful for comparing the characteristics of products from plants with different heating profiles or as a means for optimizing UHT plant performance where the heating and cooling rates are fixed.

Effects of phosphates and citrates on sediment formation in UHT goats' milk

“…Raw goats' milk was supplied by Delamere Dairies (Yew Tree Farm, Knutsford, Cheshire, UK) and Willowbrook Farm, Garford, Abingdon, UK. It was subjected to indirect UHT treatment using an APV Junior plate heat exchanger, described and characterised in terms of its temperature/ time heating profiles and corresponding B* and C* by Browning et al (2001). Four batches of raw goats' milk were processed using the same conditions of 140 8C for 2 s. Upstream homogenization during the heat treatment was at a pressure of 180 bar.…”

Instrumental measurement of milk flavour and colour

“…In addition to the above-mentioned tristimulus systems, spectral reflectance measurements (400 to 700 nm) are also a suitable estimate of degree of Instrumental measurement of milk flavour and colour 197 whiteness in milk (Nelson, 1948;Quin Äones et al, 1997;Solah et al, 2007). Some recent applications of colorimetric and spectrophotometric systems for measurement of colour in milk products can be found in the published literature (Nielsen et al, 1997;Browning et al, 2001;Gervilla et al, 2001;Nozie Áre et al, 2006;Solah et al, 2007;Popov-Raljic  et al, 2008).…”

“…Several factors are known to promote browning reactions in milk products, including use of excessive processing temperatures and adverse storage conditions. Heating of fluid milk has two main effects on its colour: at moderate temperatures (65ëC) or immediately after a UHT process an initial`whitening' may occur, while at high temperatures (>90ëC) browning readily occurs due to the Maillard reaction (Burton, 1955(Burton, , 1956Kessler and Fink, 1986;Rhim et al, 1988;Singh and Creamer, 1992;Browning et al, 2001;Popov-Raljic  et al, 2008). The increased rate of the Maillard reaction in concentrated and dried milks is due to the lower water activities and increased concentrations of reactant molecules in these products (van Boekel, 1998).…”

Proteolysis of milk heated at high temperatures by native enzymes analysed by trinitrobenzene sulphonic acid (TNBS) method

“…Raw milk was obtained from the Centre of Dairy Research (CEDAR), University of Reading, UK. It was processed on an APV junior UHT plate heat exchanger (APV, Crawley, UK), with two stages of heating involving hot water (80°C) and steam (112 to 142°C) as described (Browning et al 2001). A constant flow rate was used, giving a residence time of 2 s in the holding section at 110, 120, 130 and 142°C but 15 s at 85°C.…”