Hilton Deeth - Academia.edu (original) (raw)

Papers by Hilton Deeth

Critical Reviews in Food Science and Nutrition, Feb 24, 2009

Biogenic amines are non-volatile amines formed by decarboxylation of amino acids. Although many b... more Biogenic amines are non-volatile amines formed by decarboxylation of amino acids. Although many biogenic amines have been found in fish, only histamine, cadaverine, and putrescine have been found to be significant in fish safety and quality determination. Despite a widely reported association between histamine and scombroid food poisoning, histamine alone appears to be insufficient to cause food toxicity. Putrescine and cadaverine have been suggested to potentiate histamine toxicity. With respect to spoilage on the other hand, only cadaverine has been found to be a useful index of the initial stage of fish decomposition. The relationship between biogenic amines, sensory evaluation, and trimethylamine during spoilage are influenced by bacterial composition and free amino acid content. A mesophilic bacterial count of log 6-7 cfu/g has been found to be associated with 5 mg histamine/100 g fish, the Food and Drug Administration (FDA) maximum allowable histamine level. In vitro studies have shown the involvement of cadaverine and putrescine in the formation of nitrosamines, nitrosopiperidine (NPIP), and nitrosopyrrolidine (NPYR), respectively. In addition, impure salt, high temperature, and low pH enhance nitrosamine formation, whereas pure sodium chloride inhibits their formation. Understanding the relationships between biogenic amines and their involvement in the formation of nitrosamines could explain the mechanism of scombroid poisoning and assure the safety of many fish products.

International Dairy Journal, Oct 1, 2021

Abstract Heat treatments are used extensively in the dairy industry, primarily to inactivate bact... more Abstract Heat treatments are used extensively in the dairy industry, primarily to inactivate bacteria but also to inactivate enzymes that can cause detrimental effects. In addition, some enzymes have attracted attention as markers of particular heat processes. The current knowledge of the effects of different heat treatments on the various enzymes in milk, both indigenous and endogenous (bacterial), has been gained from extensive investigations over many years. This review collates the published information on the heat stability of 23 indigenous and two bacterial enzymes of significance in the dairy industry. The indigenous enzymes show a wide range of heat stabilities with most being totally inactivated in the range 70–100 °C and the remainder requiring higher-temperature treatments for total inactivation. Many of the bacterial enzymes show higher heat stability than all the indigenous enzymes and are not inactivated by even the most intense heat treatments used in the dairy industry.

Australian Journal of Dairy Technology, Jun 16, 1975

2-5 ml milk or 1 ml cream are mixed with 10 ml isopropanol/petroleum ether/4N H2SO4 (40:10:1) in ... more 2-5 ml milk or 1 ml cream are mixed with 10 ml isopropanol/petroleum ether/4N H2SO4 (40:10:1) in a 35 ml test tube, 6 ml petroleum ether + 4 ml water are added and the tube is shaken vigorously for 15 s. An aliquot of the upper layer is titrated with 0.02N methanolic KOH ...

Food Chemistry, May 1, 2012

Milk proteins undergo chemical changes such as lactosylation, deamidation and protein cross-linki... more Milk proteins undergo chemical changes such as lactosylation, deamidation and protein cross-linking during processing and storage of milk products. A proteomic technique combining two-dimensional gel electrophoresis and mass spectrometry was used to investigate chemical modifications to proteins, in milk protein concentrate (MPC80), during storage. Lactosylation, deamidation and protein cross-linking were observed on 2-DE gels. They were storage temperature-, humidity-and time-dependent. Lactosylated whey proteins were well separated on 2-DE in vertical stacks of spots. The masses of the spots varied by multiples of 324, indicating the attachment of lactose to lysine residues in the proteins. The trypsin-digested spots of a-lactalbumin were analysed by MALDI-TOF mass spectrometry, which indicated multiple lactosylation sites. The lactose adducts on gels were quantified by image analysis, allowing development of adducts over time to be monitored. The results show that proteomics can be used for the detection and quantification of chemical modifications to proteins in stored MPC80.

International Dairy Journal, Jun 1, 2009

Springer eBooks, 1983

The lipolytic enzymes in milk and milk products that can impart rancidity to the products are dis... more The lipolytic enzymes in milk and milk products that can impart rancidity to the products are discussed. The major endogenous milk enzyme is a lipoprotein lipase and the major microbial lipases are produced by psychrotrophic bacteria. Causes and consequences of hydrolytic ...

Journal of Dairy Research, May 23, 2005

High pressure homogenisation (HPH) is a novel dairy processing tool, which has many effects on en... more High pressure homogenisation (HPH) is a novel dairy processing tool, which has many effects on enzymes, microbes, fat globules and proteins in milk. The effects of HPH on milk are due to a combination of shear forces and frictional heating of the milk during processing; the relative importance of these different factors is unclear, and was the focus of this study. The effect of milk inlet temperature (in the range 10–50 °C) on residual plasmin, alkaline phosphatase, lactoperoxidase and lipase activities in raw whole bovine milk homogenised at 200 MPa was investigated. HPH caused significant heating of the milk; outlet temperature increased in a linear fashion (0·5887 °C/°C, R2=0·9994) with increasing inlet temperature. As milk was held for 20 s at the final temperature before cooling, samples of the same milk were heated isothermally in glass capillary tubes for the same time/temperature combinations. Inactivation profiles of alkaline phosphatase in milk were similar for isothermal heating or HPH, indicating that loss of enzyme activity was due to heating alone. Loss of plasmin and lactoperoxidase activity in HPH milk, however, was greater than that in heated milk. Large differences in residual lipase activities in milks subjected to heating or HPH were observed due to the significant increase in lipase activity in homogenised milk. Denaturation of β-lactoglobulin was more extensive following HPH than the equivalent heat treatment. Inactivation of plasmin was correlated with increasing fat/serum interfacial area but was not correlated with denaturation of β-lactoglobulin. Thus, while some effects of HPH on milk are due to thermal effects alone, many are induced by the combination of forces and heating to which the milk is exposed during HPH.

Journal of Food Protection, Dec 1, 1980

This review considers the physical and chemical changes which occur during yogurt manufacture as ... more This review considers the physical and chemical changes which occur during yogurt manufacture as a result of processing and microbial fermentation. Changes produced during processes, such as heat treatment and physical manipulations, are reviewed. Microbial fermentation is discussed in terms of the characteristics of the yogurt organisms, Lactobacillus bulgaricus and Streptococcus thermophilus, and the biochemical reactions involved in carbohydrate metabolism, flavor production, proteolysis and lipolysis.

Wiley-Blackwell eBooks, Feb 20, 2009

Page 1. 3 Microbiology of Raw and Market Milks V. Touch and HC Deeth 3.1 Introduction Milk is an ... more Page 1. 3 Microbiology of Raw and Market Milks V. Touch and HC Deeth 3.1 Introduction Milk is an ideal medium for the growth of many organisms, having a high water content and abundant nutrients, and being nearly neutral pH (6.4–6.8). ...

Springer eBooks, 2016

Sterilised milk and milk products are produced by intense heat treatments and are stored at ambie... more Sterilised milk and milk products are produced by intense heat treatments and are stored at ambient temperature for several months. These conditions present a considerable challenge to the stability of their protein components. Several changes occur during the heat treatment, usually more during in-container sterilisation than UHT treatment, and some changes continue during storage. Most are time- and temperature-dependent and some are pH-dependent. The major chemical changes are denaturation of whey proteins, covalent cross-linking of proteins, redistribution of proteins between the colloidal and serum phases, lactosylation and subsequent Maillard reactions, degradation of individual amino acids via deamidation and dephosphorylation as well as generation of volatile sulfur compounds, and proteolysis by indigenous and bacterial proteinases. Physical changes also occur, including deposit formation during heating, and further sediment formation and gelation during storage. The mineral fraction plays an important role in some of these reactions. The changes to proteins have implications for the nutritional status of the product. There is a reduction in bioavailability of essential amino acids, particularly lysine, and formation of potentially toxic compounds resulting from Maillard reactions and protein cross-linking. However, the proteins in some sterilised products may be more digestible due to physical changes causing increased accessibility to digestive proteinases.

Journal of Food Engineering, Oct 1, 2014

Australian Journal of Experimental Agriculture, 2006

Milk obtained from cows on 2 subtropical dairy feeding systems were compared for their suitabilit... more Milk obtained from cows on 2 subtropical dairy feeding systems were compared for their suitability for Cheddar cheese manufacture. Cheeses were made in a small-scale cheesemaking plant capable of making 2 blocks (about 2 kg each) of Cheddar cheese concurrently. Its repeatability was tested over 10 separate cheesemaking days with no significant differences being found between the 2 vats in cheesemaking parameters or cheese characteristics. In the feeding trial, 16 pairs of Holstein-Friesian cows were used in 2 feeding systems (M1, rain-grown tropical grass pastures and oats; and M5, a feedlot, based on maize/barley silage and lucerne hay) over 2 seasons (spring and autumn corresponding to early and late lactation, respectively). Total dry matter, crude protein (kg/cow.day) and metabolisable energy (MJ/cow.day) intakes were 17, 2.7, and 187 for M1 and 24, 4, 260 for M5, respectively. M5 cows produced higher milk yields and milk with higher protein and casein levels than the M1 cows, but the total solids and fat levels were similar (P>0.05) for both M1 and M5 cows. The yield and yield efficiency of cheese produced from the 2 feeding systems were also not significantly different. The results suggest that intensive tropical pasture systems can produce milk suitable for Cheddar cheese manufacture when cows are supplemented with a high energy concentrate. Season and stage of lactation had a much greater effect than feeding system on milk and cheesemaking characteristics with autumn (late lactation) milk having higher protein and fat contents and producing higher cheese yields.

Journal of Dairy Science, Jul 1, 1983

International Dairy Journal, Aug 1, 2017

This review draws attention to the significance of magnesium in milk, both the technical and huma... more This review draws attention to the significance of magnesium in milk, both the technical and human health aspects. Magnesium has been subject to less research than calcium in both aspects. Magnesium is present in cows' milk in ~10% of the concentration of calcium. About two-thirds of the magnesium is soluble, whereas about one third of calcium is soluble. Although magnesium is less significant than calcium in dairy systems, it warrants more investigation. Magnesium plays numerous physiological roles in the human body and is implicated in many critical health issues such as metabolic syndrome and skeletal muscle loss. Despite its well-established significance in health, magnesium is often reported as an under-consumed nutrient. Milk and dairy products are already one of the main sources of dietary magnesium. There is an opportunity to develop milk and dairy products as efficient vehicles for supplementary dietary magnesium delivery with more research into fortification options.

Journal of Dairy Research, Oct 1, 1978

The amount of damage caused to the milk-fat globule by mechanical agitation of raw milk was asses... more The amount of damage caused to the milk-fat globule by mechanical agitation of raw milk was assessed by several methods and related to the level of induced lipolysis resulting from the agitation. The results obtained by measuring the amount of 'free' fat formed, the percentage of fat in the skim-milk phase after separation, and the increase in the proportion of alkaline phosphatase associated with the skim-milk phase, showed little correlation with the level of lipolysis induced by agitation over a range of conditions. However, the level of induced lipolysis showed good correlation with the amount of lipolysis caused by addition of an exogenous lipase (from Candida cylindraceae) to the agitated milk. It is concluded that classical methods of assessing milk-fat globule damage are unsuitable for predicting the amount of fat available for lipase action and the lipolytic potential of raw milk subjected to mechanical agitation.

Journal of Dairy Research, Oct 1, 1977

SummarySeveral factors which influence the shape of activation curves relating the degree of agit... more SummarySeveral factors which influence the shape of activation curves relating the degree of agitation-induced lipolysis in raw milk to the temperature of agitation were investigated. Curves of the type previously reported (Fitz-Gerald, 1974) containing a maximum at 12–15 °C resulted from low speed agitation with incorporation of air, with fresh (< 12-h old) milk, with milk of fat content ≥ 3·0 % approx. and by low temperature incubation of activated milks. Activation curves containing no distinct maximum at 12–15 °C were obtained from high speed agitation and homogenization, with milks of low fat contents and with aged (≥ 24-h old) milk. Agitation at low temperatures resulted in a maximum degree of activation in fresh milk after 2–4 h cold storage.During agitation of raw milk redistribution of lipase activity between the cream and skim-milk phases occurred. The extent of redistribution depended on the time and temperature of agitation. Cream prepared from milk agitated at low temperatures contained lipase activity several times greater than cream from unactivated milk. The practical significance of this effect is discussed.