Thermal Food Processing

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Thermal Processing of Dairy Products 269 TABLE 9.1 Types of Heat Treatment Applied to Milk and Their Microbiological Effects Typical Microbial Quality Microbiological Effect Heat Exchanger Typical Conditions Process Thermization 57–68°C for 15 sec PHE Destroys psychrotrophs 3–4 log reduction in psychrotrophsa Pasteurization 63°C for 30 min Batch Destroys vegetative pathogens Total plate count < 100,000 cfu/mlb Pasteurization 72–74°C for 15–30 sec PHE Destroys vegetative pathogens Total plate count < 100,000 cfu/mlb Yogurt mix heating 85–95°C for 2–30 min PHE/THE Destroys all pathogens and most spores — Preheating for producing 70–135°C for 1 sec– PHE/THE/Other Depends on treatment — milk powder 5 min High-temperature 120–130 for
270 Thermal Food Processing: New Technologies and Quality Issues applied to it. Many properties of milk (sensory, nutritional, and physicochemical) consequently change as a result of thermal processing. Perhaps the most significant changes on heating milk are those that involve proteins. Most (70 to 80%) of the protein in milk is casein, a family of four largely hydrophobic proteins (α s1-, α s2-, β-, and κ-caseins). As is the case for many hydrophobic substances found in an aqueous environment, the caseins are found in milk in colloidal micelles (ranging from 50 to 500 nm in size (average, ~120 nm), with an average mass of ~10 8 Da; there are 10 14 to 10 16 micelles ml –1 milk). One of the caseins, κ-casein, is a glycoprotein with a hydrophilic sugarrich C-terminal (often called the glycomacropeptide (GMP)); κ-casein is found at the surface of the micelle, where the GMP protrudes into the serum (forming the so-called hairy layer) and stabilizes the micelle by acting in a role analogous to the amphiphilic nature of a classical emulsifying agent. The hairy layer is negatively charged and is largely responsible for the steric repulsion that prevents casein micelles from aggregating. The remainder (20 to 30%) of the proteins in milk are the so-called whey proteins, which are globular proteins found in the serum (aqueous) phase of milk; the major whey proteins are β-lactoglobulin (β-lg) and α-lactalbumin (α-la). In terms of thermal processing, β-lg is of particular significance; due to an uneven number of cysteine residues, β-lg possesses a free thiol group that, when the protein is in the native state, is located within the interior of the structure of the molecule. Heating to temperatures of >75°C, however, results in unfolding of the molecule and exposure of the thiol group, which can then undergo thiol-disulfide interchange reactions with disulfide bond-containing proteins (e.g., β-lg itself, α-la, κ- and α s2-caseins, milk fat globule membrane proteins, and the indigenous milk alkaline proteinase, plasmin). Such interactions have profound implications for the quality of heated milk and dairy products such as yogurt. For example, binding of denatured β-lg to the casein micelle, via disulfide bond formation with κ-casein, fundamentally and negatively affects the rennet coagulation properties of milk, as will be discussed later. Denatured β-lg may also associate with κ-casein via hydrophobic interactions. Exposure of free thiol groups on denaturation of β-lg results in a cooked flavor of the milk, while providing antioxidant activity. Interactions of denatured β-lg with plasmin greatly reduce the proteolytic activity in milk. The inactivation of milk enzymes is an intensively researched consequence of heating milk, due to the use of such enzymes as indices of the severity of heat treatment applied, as will be discussed in more detail later in this chapter. Severe heating has a number of specific effects on the caseins, including dephosphorylation, deamidation of glutamine and arginine residues, and cleavage and formation of covalent cross-links; these changes may result in protein–protein interactions, which contribute to thermal instability. Heat causes some alterations to the mineral balance in milk; for example, heating milk at medium or high temperatures causes precipitation of calcium phosphate and reduces calcium ion activity. 15 Heating milk also affects lactose, the nature and extent of such effects depending on environmental conditions and the severity of heating; heat-induced changes in lactose include degradation to
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Thermal Food Processing
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87. Polysaccharide Association Stru
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133. Handbook of Frozen Foods, edit
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Published in 2006 by CRC Press Tayl
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Various alternative thermal process
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Professor Sun is a fellow of the In
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Antonio Martínez Instituto de Agro
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Contents Part I: Modeling of Therma
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Chapter 17 Pressure-Assisted Therma
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1 CONTENTS Thermal Physical Propert
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Thermal Physical Properties of Food
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2 CONTENTS Heat and Mass Transfer i
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Heat and Mass Transfer in Thermal F
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5 CONTENTS Modeling Thermal Process
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Modeling Thermal Processing Using C
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6 CONTENTS Thermal Processing of Me
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Thermal Processing of Meat Products
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7 CONTENTS Thermal Processing of Po
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Thermal Processing of Poultry Produ
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UHT Thermal Processing of Milk 319
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11 CONTENTS Thermal Processing of C
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Thermal Processing of Canned Foods
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12 CONTENTS Thermal Processing of R
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Thermal Processing of Ready Meals 3
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14 CONTENTS Ohmic Heating for Food
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Ohmic Heating for Food Processing 4
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15 CONTENTS Radio Frequency Dielect
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Radio Frequency Dielectric Heating
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16 CONTENTS Infrared Heating Noboru
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Infrared Heating 495 0.78 1.4 Far-i
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Infrared Heating 497 A black body a
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Infrared Heating 499 Spectral atten
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Infrared Heating 501 Axial Distance
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Infrared Heating 503 the calculated
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Infrared Heating 505 TABLE 16.1 Com
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Infrared Heating 507 Rotating drum
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Infrared Heating 509 Conc. of acid
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Infrared Heating 513 Degradation ra
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Infrared Heating 517 T l (K) N l /
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Infrared Heating 519 Temperature (
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Infrared Heating 521 and thawing ti
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Infrared Heating 523 15. T Takeo. F
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Infrared Heating 525 55. CM Liu, N
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638 Index Tea, 451, 510 Temperature
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640 Index Wax beans, 398, 411 Web s
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Thermal Food Processing

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