High-temperature Short-time Milk Research Articles

Microbacterium represents an emerging microorganism of concern in microfiltered extended shelf-life milk products

Growing interest in the manufacture of extended shelf-life (ESL) milk, which is typically achieved by a high temperature treatment called ultra-pasteurization (UP), is driven by distribution challenges, efforts to reduce food waste, and more. Even though high temperature, short time (HTST) pasteurized milk has a substantially shorter shelf-life than UP milk, HTST milk is preferred in the United States because consumers tend to perceive UP milk as less desirable due to the "cooked" flavor associated with high-temperature processing. While ESL beyond 21 d may be possible for HTST, the survival and outgrowth of psychrotolerant aerobic spore-forming bacteria can still be a limitation to extending shelf-life of HTST milk. Microfiltration (MF) is effective for reducing vegetative microorganisms and spores in raw milk, but it is unclear what the effects of membrane pore size, storage temperature, and milk type (i.e., skim vs whole) are on the microbial shelf-life of milk processed by both MF and HTST pasteurization. To investigate these factors, raw skim milk was MF using different pore sizes (0.8 μm or 1.2 μm), and then MF skim milk and standardized whole milk [MF skim with heat-treated (85°C for 20 s) cream] were HTST pasteurized at 75°C for 20 s. Subsequently, milk was stored at 3, 6.5, or 10°C and total bacteria counts were measured for up to 63 d. An ANOVA indicated that mean bacterial concentrations between storage temperatures were significantly different from each other, with mean maximum observed concentrations of 3.67, 5.33, and 8.08 log10 cfu/mL for storage temperatures 3, 6.5, and 10°C, respectively. Additionally, a smaller difference in mean maximum bacterial concentrations throughout shelf-life was identified between pore sizes (<1 log cfu/mL), but no significant difference was attributed to milk type. An unexpected outcome of this study was the identification of Microbacterium as a major contributor to the bacterial population in MF ESL milk. Microbacterium is a psychrotolerant, thermoduric gram-positive, non-spore forming rod with a small cell size (∼0.9 μm length and ∼0.3 μm width), which was able to permeate the membranes used in this study, survive HTST pasteurization, and then grow at refrigeration temperatures. While spores continue to be a key concern for the manufacture of MF, ESL milk, our study demonstrates the importance of other psychrotolerant, thermoduric bacteria such as Microbacterium to these products.

Shelf-life storage temperature has a considerably larger effect than high-temperature, short-time pasteurization temperature on the growth of spore-forming bacteria in fluid milk

In the absence of postpasteurization contamination, psychrotolerant, aerobic spore-forming bacteria that survive high-temperature, short-time (HTST) pasteurization, limit the ability to achieve HTST extended shelf-life milk. Therefore, the goal of the current study was to evaluate bacterial outgrowth in milk pasteurized at different temperatures (75, 85, or 90°C, each for 20 s) and subsequently stored at 3, 6.5, or 10°C. An initial ANOVA of bacterial concentrations over 14 d of storage revealed a highly significant effect of storage temperatures, but no significant effect of HTST. At d 14, average bacterial counts for milk stored at 3, 6.5, and 10°C were 1.82, 3.55, and 6.86 log10 cfu/mL, respectively. Time to reach 1,000,000 cfu/mL (a bacterial concentration where consumers begin to notice microbially induced sensory defects in fluid milk) was estimated to be 68, 27, and 10 d for milk stored at 3, 6.5, and 10°C, respectively. Out of 95 isolates characterized with rpoB allelic typing, 6 unique genera, 15 unique species, and 44 unique rpoB allelic types were represented. The most common genera identified were Paenibacillus, Bacillus, and Lysinibacillus. Nonmetric multidimensional scaling identified that Bacillus was significantly associated with 3 and 10°C, whereas Paenibacillus was consistently found across all storage temperatures. Overall, our data show that storage temperature has a substantially larger effect on fluid milk shelf life than HTST and suggests that abuse temperatures (e.g., storage at 10°C) allow for growth of Bacillus species (including Bacillus cereus genomospecies) that do not grow at lower temperatures. This indicates that stringent control of storage and distribution temperatures is critical for producing extended shelf-life HTST milk, particularly concerning new distribution pathways for HTST pasteurized milk (e.g., electronic commerce), and when enhanced control of spores in raw milk is not feasible.

Control of high temperature short time milk pasteurization plant with centralized and decentralized linear quadratic regulators

ABSTRACT Precise temperature control in each stage of the pasteurization process is important to deactivate pathogenic bacteria, and any temperature fluctuations during milk processing may affect the nutritional value and quality of the milk. Hence, maintaining stable temperature and minimizing disturbance effects is essential for improved quality of the milk. This necessitates an efficient controller that may provide precise temperature control despite process disturbances. Here, a mathematical model representing the high-temperature short-time (H.T.S.T) milk pasteurization process is simulated. The proposed model is simulated without a pre-cooling stage, thereby contributing to energy minimization but without compromising the operating conditions of the process. The design of a Linear Quadratic Regulator (L.Q.R)-based centralized and decentralized control for the H.T.S.T milk pasteurization process is implemented. The L.Q.R exhibits good results at disturbance rejection and targets mainly the objective function minimization. So, minimizing the energy is the prime objective of the L.Q.R. The centralized and decentralized L.Q.R structures were designed for the proposed plant, and the control scheme efficiencies are analyzed. The juxtaposition of these two control schemes reveals that the decentralized L.Q.R structure outperforms the centralized structure for the H.T.S.T milk pasteurization process.

Comparative study on the microstructure and functional properties of casein in goat milk processed by different methods

SummaryThis work compared the thermal stability, microstructure and functional properties of casein (CN) in goat milk processed by different methods, including homogenisation, low‐temperature long‐time (LTLT), high‐temperature short‐time (HTST), ultrapasteurisation (UP) and ultrahigh temperature (UHT) treatment. The greatest development of CN‐whey protein complexes was observed in LTLT goat milk and the least in HTST goat milk. The CN micelles in LTLT, UP and UHT milk were more obviously changed than the CN micelles in HTST milk, and the random coil content increased significantly after the homogenisation, UP and UHT treatments. The homogenisation had a significant effect on the functional properties of CN. In addition, the most obvious changes in the properties of CN were observed in LTLT and UHT goat milk. The results suggested that homogenisation, pasteurisation and UHT can cause effective changes in the functional properties of CN in goat milk that facilitate its application in the milk industry.

Identification of high temperature short time milk pasteurization unit

AbstractThis research pertains to the development of a dynamic‐model and identification of parameters for high‐temperature‐short‐time (HTST) pasteurization process using plate‐heat‐exchangers for precise controller scheme for this process. Real‐time HTST process consists of three integrated sections, (a) plate‐heat‐exchanger engaged in regeneration, heating and cooling (b) holding tank, and (c) holding tube. The models for these sections are identified using Matlab. The dynamics of the HTST process using the first‐principle method consisting of two inputs one‐output model is derived. The parameters of the dynamic model are identified using the autoregressive‐exogenous linear identification technique, ARMAX, and subspace system identification to predict the outlet temperature of HTST process. Finally, a dynamic‐model, relating exit temperature to input enthalpy is obtained from the closed‐loop process input–output data, using a nonlinear least‐square‐estimation technique. The quality of prediction of linear‐model structures is checked using plant's data. The results obtained from the linear‐models are in good agreement with plant‐data.Practical applicationMilk should be free from toxins and pathogens and also it must retain all nutrients and vitamins with extended period of storage life. To achieve the above said criteria, milk is heated to a particular temperature for a brief time then cooling it down once more quickly. Moreover, to avoid superheating, the temperature needs to be controlled. As model‐based‐control perform satisfactorily, tuning of controllers can be done using model parameters of this milk‐heating process. These model parameters are obtained from on‐line identification of the predicted model using real time plant input–output data. This paper deals with identification of model parameters for the milk pasteurization process. The formulated model equations are also validated, which will help in optimizing the operating parameters and scale‐up design.

Effects of industrial heat treatments on the kinetics of inactivation of antimicrobial bovine milk xanthine oxidase

Milk is a source of antimicrobial systems such as xanthine oxidoreductase, which has been proposed to modulate the oral and gut microbiota of infants. Heat treatments are applied to milk to ensure its microbial safety, however, the effects of heat on this antimicrobial enzyme are not known. The effects of batch pasteurization (BP), high-temperature short time (HTST), and ultra high temperature (UHT) on kinetics of inactivation of xanthine oxidase and its antimicrobial properties were determined. Xanthine oxidase activity was preserved by HTST (100%). Partial (8%) and nearly complete (95%) enzyme inactivation were observed for BP and UHT milks, respectively. Km values of 100 μM and Vmax values of 6.85, 5.12, 6.31, and 0.40 μmol/min/mg were determined for xanthine oxidase in raw, BP, HTST, and UHT milks, respectively. These results demonstrate that xanthine oxidase maintains apparent affinity and activity for its substrate when milk is treated by BP and HTST and yet the enzyme is inactivated with UHT. To investigate heat treatment-induced alterations in the biological activity of xanthine oxidase, heat treated milks were compared to raw milk for their ability to inhibit the growth of S. aureus. Raw, BP, and HTST milk xanthine oxidase efficiently inhibited S. aureus growth. However, these antibacterial properties were lost when milk was subjected to UHT. These results demonstrate that HTST and BP preserves bovine milk xanthine oxidase activity compared with UHT and that, the judicious selection of thermal treatments could be exploited to preserve the antimicrobial properties of bovine milk.

Energy, exergy and exergoeconomic analysis of high temperature short time milk pasteurisation plant

India produces 19.54% of the total annual milk production of the entire world (819 MT) with yearly rise of 3.6%. The thermal and electrical energies consume 10%-20% of manufacturing cost of pasteurised milk. In the present work, energy, exergy and exergoeconomic appraisals of skim milk pasteurisation plant have been performed. The exergy gauge registered an exergy efficiency of 68.84% with 35% exergy recovery potential. The analysis revealed that relative irreversibility ratio of regeneration-3 (7.87%) was higher than regeneration-2 (4.24%) followed by regeneration-1 (1.25%), which represented their excellent sustainability characteristics. The thermoeconomic analysis has identified the immensity of exergoeconomic indices such as total operating cost rate, exergoeconomic factor and percentage relative cost difference. The exergoeconomic factor was reported to be most significant in holding coil (62.45%), heat exchanger (49.25%) and regeneration-1 (20.18%). The high and low values of exergoeconomic factor magnify the role of capital investment and thermodynamic inefficiencies respectively.

Energy, exergy and exergoeconomic analysis of high temperature short time milk pasteurisation plant

Energy, exergy and exergoeconomic analysis of high temperature short time milk pasteurisation plant

The influence of ultra-pasteurization by indirect heating versus direct steam injection on skim and 2% fat milks

Fluid milk is traditionally pasteurized by high temperature, short time (HTST) pasteurization, which requires heating to at least 72°C for 15 s. Ultra-pasteurization (UP) extends milk shelf life and is defined as heating to at least 138°C for 2 s. The UP process can be done by indirect heating (IND) or by direct steam injection (DSI). The influence of these 2 UP methods on milk flavor has not been widely investigated. The objective of this study was to compare the effect of HTST, IND-UP, and DSI-UP on sensory perception of fluid milk. Raw skim and standardized 2% milks were pasteurized at 140°C for 2.3 s by IND or DSI or by HTST (78°C, 15 s) and homogenized at 20.7 MPa. The processed milks were stored in light-shielded opaque high-density polyethylene containers at 4°C and examined by descriptive analysis and microbial analysis on d 3, 7, and 14. Furosine and serum protein denaturation analyses were performed on d 0 and 14 as an indicator of heat treatment. Last, consumer acceptance testing was conducted at d 10, with adults (n = 250) and children (ages 8 to13 y, n = 100) who were self-reported consumers of skim or 2% milk; consumers only received samples for either skim or 2% milk. The entire experiment was repeated in triplicate. Milks treated by HTST had lower cooked flavor than either UP milk. Milks heated by DSI-UP were characterized by sulfur or eggy and cooked flavors, whereas IND-UP milks had higher sweet aromatic and sweet taste compared with DSI-UP milk. Aromatic flavor intensities of all milks decreased across 14 d of storage. Furosine concentrations and serum protein denaturation were highest for the IND treatments, followed by DSI and HTST. Furosine content in both skim and 2% milk increased with time, but the increase was faster in IND-UP skim milk. Adult and child consumers preferred HTST milk over either UP milk, regardless of fat content. Ultra-pasteurization by IND or DSI did not affect consumer acceptance at 10 d postprocessing, but traditional HTST milks were preferred by consumers of all ages.

A survey of the quality of extended shelf life (ESL) milk in relation to HTST and UHT milk

Thirty milk samples [high‐temperature short‐time (HTST) milk, extended shelf life (ESL) milk (directly heated, indirectly heated, microfiltered), ultra‐high temperature milk] from 17 German dairies were analysed. Total viable counts of directly or indirectly heated ESL milk were significantly lower than those in microfiltered ESL and HTST milk. Evaluation of indigenous enzyme activity revealed sufficient heat treatments in all milk samples. The manufacturing processes were differentiated by estimating furosine and acid soluble whey proteins. Sensory examinations revealed a preference for HTST heated and microfiltered ESL milk. However, a significant discrimination of drinking milk types was not possible. Vitamin losses were not detected, and concentrations of vitamins in different types of milk were comparable.

Inactivation of Bacillus anthracis spores by a combination of biocides and heating under high-temperature short-time pasteurization conditions.

The milk supply is considered a primary route for a bioterrorism attack with Bacillus anthracis spores because typical high-temperature short-time (HTST) pasteurization conditions cannot inactivate spores. In the event of intentional contamination, an effective method to inactivate the spores in milk under HTST processing conditions is needed. This study was undertaken to identify combinations and concentrations of biocides that can inactivate B. anthracis spores at temperatures in the HTST range in less than 1 min. Hydrogen peroxide (HP), sodium hypochlorite (SH), and peroxyacetic acid (PA) were evaluated for their efficacy in inactivating spores of strains 7702, ANR-1, and 9131 in milk at 72, 80, and 85 degrees C using a sealed capillary tube technique. Strains ANR-1 and 9131 were more resistant to all of the biocide treatments than strain 7702. Addition of 1,260 ppm SH to milk reduced the number of viable spores of each strain by 6 log CFU/ml in less than 90 and 60 s at 72 and 80 degrees C, respectively. After neutralization, 1,260 ppm SH reduced the time necessary to inactivate 6 log CFU/ml (TTI6-log) at 80 degrees C to less than 20 s. Treatment of milk with 7,000 ppm HP resulted in a similar level of inactivation in 60 s. Combined treatment with 1,260 ppm SH and 1,800 ppm HP inactivated spores of all strains in less than 20 s at 80 degrees C. Mixing 15 ppm PA with milk containing 1,260 ppm SH resulted in TTI6-log of 25 and 12 s at 72 and 80 degrees C, respectively. TTI6-log of less than 20 s were also achieved at 80 degrees C by using two combinations of biocides: 250 ppm SH, 700 ppm HP, and 150 ppm PA; and 420 ppm SH (pH 7), 1,100 ppm HP, and 15 ppm PA. These results indicated that different combinations of biocides could consistently result in 6-log reductions in the number of B. anthracis spores in less than 1 min at temperatures in the HTST range. This information could be useful for developing more effective thermal treatment strategies which could be used in HTST milk plants to process contaminated milk for disposal and decontamination, as well as for potential protective measures.

Acceptance of 2% Ultra-Pasteurized Milk by Consumers, 6 to 11 Years Old

The objective of this study was to determine the degree of liking of ultra-pasteurized (UP) milk by 6 to 11 year olds. For comparative purposes, 2% UP milks were evaluated along with 2% conventionally pasteurized high temperature short time (HTST) and 2% ultra high temperature (UHT) milks. A seven-point facial hedonic scale with Peryam & Kroll verbal descriptors for affective testing with children was used with the 6 year olds. For the older children, a seven-point hedonic scale with Peryam & Kroll verbal descriptors was used. The mean degree of liking of UP milk was rated as slightly below “good.” HTST milk was liked slightly more than the UHT milk, which was liked slightly more than the UP milk. How the children felt about milk, in general, significantly affected how much they liked the test milks, with all milks being influenced equally.