Process-Induced Molecular-Level Protein-Carbohydrate-Polyphenol Interactions in Milk-Tea Blends: A Review

The rapid increase in the production of powdered milk-tea blends is driven by a growing awareness of the presence of highly nutritious bioactive compounds and consumer demand for convenient beverages. However, the lack of literature on the impact of heat-induced component interactions during processing hinders the production of high-quality milk-tea powders. The production process of milk-tea powder blends includes the key steps of pasteurization, evaporation, and spray drying. Controlling heat-induced interactions, such as protein-protein, protein-carbohydrate, protein-polyphenol, carbohydrate-polyphenol, and carbohydrate-polyphenol, during pasteurization, concentration, and evaporation is essential for producing a high-quality milk-tea powder with favorable physical, structural, rheological, sensory, and nutritional qualities. Adjusting production parameters, such as the type and the composition of ingredients, processing methods, and processing conditions, is a great way to modify these interactions between components in the formulation, and thereby, provide improved properties and storage stability for the final product. Therefore, this review comprehensively discusses how molecular-level interactions among proteins, carbohydrates, and polyphenols are affected by various unit operations during the production of milk-tea powders.

The Impact of Thermal Treatment Intensity on Proteins, Fatty Acids, Macro/Micro-Nutrients, Flavor, and Heating Markers of Milk-A Comprehensive Review

Milk thermal treatment, such as pasteurization, high-temperature short-time processing, and the emerging ultra-short-time processing (<0.5 s), are crucial for ensuring milk safety and extending its shelf life. Milk is a nutritive food matrix with various macro/micro-nutrients and other constituents that are possibly affected by thermal treatment for reasons associated with processing strength. Therefore, understanding the relationship between heating strength and milk quality is vital for the dairy industry. This review summarizes the impact of thermal treatment strength on milk's nutritional and sensory properties, the synthesizing of the structural integrity and bioavailability of milk proteins, the profile and stability of fatty acids, the retention of macro/micro-nutrients, as well as the overall flavor profile. Additionally, it examines the formation of heat-induced markers, such as Maillard reaction products, lactulose, furosine, and alkaline phosphatase activity, which serve as indicators of heating intensity. Flavor and heating markers are commonly used to assess the quality of pasteurized milk. By examining former studies, we conclude that ultra-short-time-processing-treated milk is comparable to pasteurized milk in terms of specific parameters (such as whey protein behavior, furosine, and ALP contents). This review aims to better summarize how thermal treatments influence the milk matrix, guiding the dairy industry's development and balancing milk products' safety and nutritional value.

Production of low-lactose and low-serum-protein milk protein beverages using microfiltration

Our objective was to determine the effect of simultaneous removal of lactose plus low-molecular weight solutes and milk serum proteins from skim milk by microfiltration (MF) on the chemical, physical, and sensory properties of 3.4%, 7.5%, and 10.5% milk protein-based beverages before and after a direct steam injection thermal process. Skim milk was microfiltered at 50°C using 0.1-μm ceramic membranes with a diafiltration ratio of water to milk of about 2.5. Milk lactose, serum proteins, and soluble minerals were removed simultaneously to produce protein beverages containing from 3.4% to 10.5% true protein from skim milk and this process was replicated twice with different skim milks. The soluble mineral plus lactose content was very low and the aqueous phase of the beverages had a freezing point very close to water (i.e., -0.02°C). Beverage pH ranged from 7.19 to 7.41, with pH decreasing with increasing protein concentration. Overall, the beverages were whiter and blander than skim milk. When UHT processed with direct steam injection at a holding temp of 140°C for 2 to 3 s, there was some protein aggregation detected by particle size analysis (volume mean diameter of protein particles was 0.16 μm before and 22 μm after UHT). No sulfur or eggy flavor was detected, and no browning was observed, due to the UHT thermal treatment. Both apparent viscosity and sensory viscosity increased with increasing protein concentration and heat treatment.

Ultrafiltration: Impact of process temperature (7 and 50°C) on process performance and protein beverage physical, chemical, and sensory properties

Our objectives were to determine the impact of ultrafiltration (UF) of skim milk at 7 and 50°C on UF processing, lactose removal, mineral partitioning, and skim milk retentate physical, chemical, and sensory properties at 3 (3.4 7.5, and 10.5%) protein concentration with 2 different heat processing treatments high temperature short time (HTST) pasteurization and autoclave). Pasteurized skim milk was split into 2 portions and the 7°C UF processing run was done on one day and the 50°C UF processing run was done on the next day. Skim milk was ultrafiltered and diafiltered at 7 and 50°C and as permeate was removed, deionized water at 7 or 50°C was added in an equal amount by weight as permeate removed to maintain constant protein concentration in the retentate during UF until 98% or more of lactose and low molecular weight soluble milk components were removed. All skim milk-based beverage bases from the 7 and 50°C UF of skim milk were HTST (78°C for 15 s) processed or autoclaved (116°C for 6 min). The physical, chemical, and sensory properties of all treatments were measured. This process was replicated twice with a new batch of pasteurized skim milk in a different week with the 7 and 50°C UF processing runs ran in reverse order. Overall, lactose-free skim milk at 3.4, 7.5, and 10.5% protein produced by UF with DF, was more bland, more white and less heat stable (i.e., stable to retorting but not direct steam injection at 142°C for 2 to 3 s) than skim milk based on both sensory scores and instrumental measures. A 98 to 99% removal of lactose from skim milk was achieved (final lactose concentration <0.06 g/100g) with a diafiltration ratio of water to milk of about 4 to 1 was used at both 7°C and 50°C. The processing time to achieve that lactose removal from the same starting weight of milk was about twice as long when filtering at 7°C than 50°C because of the lower flux (23 versus 48 kg/m2/h). The continuous DF at constant protein concentration maintained constant flux for a processing time of 4 and 8 h at 50 and 7°C, respectively. The final freezing point of the lactose and soluble mineral reduced milk was close to that of water (-0.015°C versus -0.525°C for skim milk) and the pH of the lactose-free milk at 20°C increased from about 6.5 for skim to about 7.33 and 7.46 for UF/DF skim milk at 7 and 50°C, respectively. Removal of compounds that absorb light (in the range of 360 to 500 nm) from milk in the permeate, increased light reflectance and whiteness and decreased yellowness relative to the starting skim milk.

Heat Stability Assessment of Milk: A Review of Traditional and Innovative Methods

It is important to differentiate milk with different thermostabilities for diverse applications in food products and for the appropriate selection of processing and maintenance of manufacturing facilities. In this review, an overview of the chemical changes in milk subjected to high-temperature heating is given. An emphasis is given to the studies of traditional and state-of-the-art strategies for assessing the milk thermostability, as well as their influencing factors. Traditional subjective and objective techniques have been used extensively in many studies for evaluating thermostability, whereas recent research has been focused on novel approaches with greater objectivity and accuracy, including innovative physical, spectroscopic, and predictive tools.

Graduate Student Literature Review: Network of flavor compounds formation and influence factors in yogurt

Yogurt is popular as a natural and healthy food, but its flavor greatly affects acceptability by consumers. Flavor compounds of yogurt is generally produced by the metabolism of lactose, protein and fat, and the resulting flavors include carbonyls, acids, esters and alcohols, etc. Each flavor compounds could individually provide the corresponding flavor, or it can be combined with other compounds to form a new flavor. The flavor network was formed among the metabolites of milk components, and acetaldehyde, as the central compounds, played a role in connecting the whole network. The flavor compounds can be affected by many factors, such as the use of different raw milks, ways of homogenization, sterilization, fermentation, post ripening, storage condition and packaging materials, etc., which can affect the overall flavor of yogurt. This paper provides an overview of the volatile flavor compounds in yogurt, the pathways of production of the main flavor compounds during yogurt fermentation, and the factors that influence the flavor of yogurt including type of raw milk, processing, and storage. It also tries to provide theoretical guidance for the product of yogurt in ideal flavor, but further research is needed to provide a more comprehensive description of the flavor system of yogurt.

Identification of Aroma-active Compounds in Milk by GC×GC-O-TOF-MS Combined with Check-all-that-apply

Understanding consumers' sensory preferences for dairy products is essential. This study employed sensory analysis and instrumental techniques to analyze the flavor of pasteurized milk and ultra-high temperature (UHT) milk. There were 6 milk samples with similar fat content (4.0-4.6 g/100mL) and protein content (3.2-3.8 g/100mL). Sensory data from consumer tests was collected using CATA (n = 100) and 9-point hedonic preferences. Research showed that Chinese consumers could distinguish the flavor of the 2 types of milk, and UHT milk showed a higher preference score, which may be due to the more pronounced milky flavor and sweet taste of UHT milk. A total of 48 aroma-active compounds were sniffed through GC × GC-O-TOF-MS, among which 11 were determined as key aroma-active compounds. Correlation analysis showed that milky odor, sweetness, and aftertaste-milky were positively correlated with γ-dodecalactone and γ-nonanolactone. Cooked and oxidized taste were positively correlated with 1-octen-3-ol and E-2-octenal. This study is important for developing Chinese dairy products and exporting dairy products to China by multinational companies.

Milk beverage base with lactose removed with ultrafiltration: Effect of fat and protein concentration on sensory and physical properties

Our objectives were to determine the effect of fat (skim to whole milk) and protein (3.4%-10.5%) concentration on the sensory and physical properties of milk beverage base that had lactose and other low molecular components removed by ultrafiltration (UF). In experiment 1, a matrix of 16 treatments was produced to achieve 4 levels of lactose removal (0%, 30%, 70%, and 97%) at each of 4 fat levels (skim, 1%, 2%, and whole milk). In experiment 2, a matrix of 12 treatments was produced to achieve 4 levels of lactose removal (0%, 30%, 70%, and 97%) at each of 3 protein concentrations (3.4%, 6.5%, and 10.5% protein). Physical and sensory properties of these products were determined. Removal of >95% of milk lactose by UF required a diafiltration volume of approximately 3 times the milk volume. Lactose and low molecular weight solute removal increased whiteness across the range from skim to whole milk while decreasing viscosity and making milk flavor blander. In addition, lactose (and other low molecular weight solute) removal by UF decreased titratable acidity by more than 50% and increased milk pH at 20°C to >7.0. Future work on milk and milk-based beverages with lactose removed by UF needs to focus on interaction of the remaining milk solids with added flavorings, changing casein to whey protein ratio before removal of lactose by UF, and the effect of lactose and low molecular weight solute removal on heat stability, particularly for neutral-pH, shelf-stable milk-based beverages.

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 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°C, 6.5°C, 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°C, 6.5°C, 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 our data suggest 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.

Economic and environmental analysis of processing plant interventions to reduce fluid milk waste

With the increased awareness about the economic and environmental impact of food waste, many interventions along food supply chains have been proposed to mitigate food waste. Even though interventions used to target food waste usually revolve around logistics and operations management, we highlight a unique solution to address this issue, specifically for fluid milk. We target the intrinsic quality of fluid milk by evaluating interventions that will extend the product shelf life. We used data from a previous fluid milk spoilage simulation model, collected price and product information from retail stores, conducted an expert elicitation, and used hedonic price regressions to determine the private and social gains to the dairy processing plant when implementing 5 different interventions to extend shelf life. Our data suggest that the value of each additional day of shelf life is approximately $0.03 and indicate that increasing periodic equipment cleaning is the most cost-effective strategy for processing plants to achieve fluid milk shelf-life improvements, both from a firm's economic standpoint and from an environmental standpoint. Importantly, the approaches reported here will be valuable to help individual firms to generate customized facility and firm specific assessments that identify the most appropriate strategies for extending the shelf life of different dairy products.

A mini-review about direct steam heating and its application in dairy and plant protein processing

The world's requirement for plant protein consumption is increasing. However, their application in different foods is limited due to their low techno-functionality. Heating is the most widely used method to improve the functionality of proteins. Compared to indirect tubular or plate heating methods, direct steam injection heating (DSIH) can heat the sample much faster, thus modifying the structure and functionality of protein differently. It is used in the sterilization of milk to minimize the heat-induced denaturation of whey proteins and the loss of volatiles. By contrast, its application in producing plant protein ingredients is seldom. This review summarizes recent research using DSIH to process dairy- and plant-based proteins and proposes future research perspectives. DSIH is a promising technique for producing functional protein ingredients. It is of particular interest to overcome the techno-functional hurdles of plant protein blends using DSIH to improve their behavior in different food matrices.

Effect of dipotassium phosphate and heat on milk protein beverage viscosity and color

Our objective was to determine the effect of addition of dipotassium phosphate (DKP) at 3 different thermal treatments on color, viscosity, and sensory properties of 7.5% milk protein-based beverages during 15 d of storage at 4°C. Micellar casein concentrate (MCC) and milk protein concentrate (MPC) containing about 7.5% protein were produced from pasteurized skim milk using a 3×, 3-stage ceramic microfiltration process and a 3×, 3-stage polymeric ultrafiltration membrane process, respectively. The MCC and MPC were each split into 6 batches, based on thermal process and addition of DKP. The 6 batches were no postfiltration heat treatment with added DKP (0.15%), no postfiltration heat without added DKP (0%), postfiltration high-temperature, short time (HTST) with DKP, postfiltration HTST without DKP, postfiltration direct steam injection with DKP, and postfiltration direct steam injection without DKP. The 6 MCC milk-based beverages and the 6 MPC milk-based beverages were stored at 4°C. Viscosity, color, and sensory properties were determined over 15 d of refrigerated storage. MCC- and MPC-based beverages at 7.5% protein with and without 0.15% added dipotassium phosphate were successfully run through an HTST and direct steam injection thermal process. The 7.5% protein MCC-based beverage contained a higher calcium and phosphorus content (2,425 and 1,583 mg/L, respectively) than the 7.5% protein MPC-based beverages (2,141 and 1,338 mg/L, respectively). Pasteurization (HTST) had very little effect on beverage particle size distribution, whereas direct steam injection thermal processing produced protein aggregates with medians in the range of 10 and 175 μm for MPC beverages. A population of casein micelles at about 0.15 μm was found in both MCC- and MPC-based beverages. Larger particles in the 175-μm range were not detected in the MCC beverages. In general, the apparent viscosity (AV) of MCC beverages was higher than MPC beverages. Added DKP increased the AV of both MCC- and MPC-based beverages, while increasing heat treatment decreased AV. The AV of beverages with DKP increased during 15 d of 4°C of storage for both MCC and MPC, whereas there was very little change in AV during storage without DKP and a similar effect was observed for sensory viscosity scores. The L value of beverages was higher with higher heat treatment, but DKP addition decreased L value and sensory opacity greatly. Sulfur-eggy flavors were detected in MPC beverages, but not MCC-based beverages.

Analysis of Volatile Organic Compounds in Milk during Heat Treatment Based on E-Nose, E-Tongue and HS-SPME-GC-MS

Volatile organic compounds (VOCs) make up milk flavor and are essential attributes for consumers to evaluate milk quality. In order to investigate the influence of heat treatment on the VOCs of milk, electronic nose (E-nose), electronic tongue (E-tongue) and headspace solid-phase microextraction (HS-SPME)-gas chromatography-mass spectrometry (GC-MS) technology were used to evaluate the changes in VOCs in milk during 65 °C heat treatment and 135 °C heat treatment. The E-nose revealed differences in the overall flavor of milk, and the overall flavor performance of milk after heat treatment at 65 °C for 30 min is similar to that of raw milk, which can maximize the preservation of the original taste of milk. However, both were significantly different to the 135 °C-treated milk. The E-tongue results showed that the different processing techniques significantly affected taste presentation. In terms of taste performance, the sweetness of raw milk was more prominent, the saltiness of milk treated at 65 °C was more prominent, and the bitterness of milk treated at 135 °C was more prominent. The results of HS-SPME-GC-MS showed that a total of 43 VOCs were identified in the three types of milk-5 aldehydes, 8 alcohols, 4 ketones, 3 esters, 13 acids, 8 hydrocarbons, 1 nitrogenous compound, and 1 phenol. The amount of acid compounds was dramatically reduced as the heat treatment temperature rose, while ketones, esters, and hydrocarbons were encouraged to accumulate instead. Furfural, 2-heptanone, 2-undecanone, 2-furanmethanol, pentanoic acid ethyl ester, 5-octanolide, and 4,7-dimethyl-undecane can be used as the characteristic VOCs of milk treated at 135 °C. Our study provides new evidence for differences in VOCs produced during milk processing and insights into quality control during milk production.

E-nose, E-tongue Combined with GC-IMS to Analyze the Influence of Key Additives during Processing on the Flavor of Infant Formula

In order to analyze the influence of key additives during processing on the flavor of infant formula, the headspace-gas chromatography-ion mobility spectrometry, electronic tongue, and electronic nose techniques were used to evaluate flavor during the processing of stage 1 infant formula milk powder (0-6 months), including the analysis of seven critical additives. A total of 41 volatile compounds were identified, involving 12 aldehydes, 11 ketones, 9 esters, 4 olefins, 2 alcohols, 2 furans, and 1 acid. The electronic nose metal oxide sensor W5S had the highest response, followed by W1S and W2S, illustrating that these three sensors had great effects on distinguishing samples. The response results of the electronic tongue showed that the three sensory attributes of bitter, salty, and umami, as well as the richness of aftertaste, were more prominent, which contributed significantly to evaluating the taste profile and distinguishing among samples. Raw milk is an essential control point in the flavor formation process of stage 1 infant formula milk powder. Demineralized whey powder is the primary source of potential off-flavor components in hydrolyzed milk protein infant formula. This study revealed the quality characteristics and flavor differences of key additives in the production process of stage 1 infant formula milk powder, which could provide theoretical guidance for the quality control and sensory improvement of the industrialized production of infant formula.

Comparison of the Effects of 5-Hydroxymethylfurfural in Milk Powder Matrix and Standard Water on Oxidative Stress System of Zebrafish

5-Hydroxymethylfurfural (5-HMF) and furfural (FF) are products of the maillard reaction (MR) in milk powder and their safety is controversial. The concentration changes of 5-HMF and FF after a period of cold storage were determined by high-performance liquid chromatography (HPLC). Then, we compared the toxicity effects of 5-HMF (2, 20, or 200 μM) in milk powder matrix and standard water on the oxidative stress system of zebrafish embryos. The results showed that the concentration of 5-HMF was stable, and the concentration of FF degraded over time. 5-HMF-exposed zebrafish embryos had a LC₅₀ value of 961 μM for 120 h. High-concentration of 5-HMF exposure resulted in developmental toxicity and induced oxidative stress. 5-HMF exposure resulted in low expression of gstr gene at 200 μM in both matrices. Moreover, sod, cat, gstr, and gpxla genes were differentially highly expressed in other groups or showed no significant difference. Residual levels in all groups were well below the exposed dose, with a maximum value of only 0.4‱. These results provided a theoretical basis for understanding the effects of 5-HMF exposure in milk powder matrix on the oxidative stress system and suggested that the presence of 5-HMF in our daily consumption of milk powder does not produce significant toxic effects and need not be overstressed.

Research Status and Prospect for Vibration, Noise and Temperature Rise-Based Effect of Food Transport Pumps on the Characteristics of Liquid Foods

In the field of food processing, the processing of liquid foods has always played an important role. Liquid foods have high requirements for the processing environment and equipment. As the core equipment in liquid foods processing, food transport pumps are widely used in liquid foods production, processing and transportation. Most liquid foods are non-Newtonian and vulnerable to vibration, noise, and temperature rise produced by rotary motions of food transport pumps in operation, which can finally affect foods safety. Therefore, this review summarizes the impact of mechanical vibration, noise, and temperature rise on liquid food products, with the aim of ensuring food safety while designing a cleaner, safer and more reliable food transport pumps in the future.

Effects of micellar casein concentrate purity and milk fat on sulfur/eggy flavor in ultrapasteurized milk-based beverages

Our objectives were to determine the level of milk-derived whey protein (MDWP) removal necessary to achieve no detectable sulfur/eggy flavor in ultrapasteurized fat-free micellar casein concentrate (MCC) beverages (6.5% protein) and in the same beverages containing 1 and 2% milk fat. Micellar casein concentrate with 95% MDWP removal was produced from skim milk (50°C) with a 3×, 3-stage ceramic microfiltration (MF) process using 0.1-µm pore size graded permeability membranes (n = 3). In experiment 1, MCC-based beverages at about 6.5% (wt/wt) true protein were formulated at a fat content of 0.15% fat (wt/wt) at 4 different levels of MDWP removal percentages (95.2%, 91.0%, 83.2%, and 69.3%). In experiment 2, a similar series of beverages at 3 MDWP removal percentages (95.2%, 83.2%, and 69.3%) with 0.1, 1, and 2% fat content were produced. The purity (or completeness of removal of whey protein by MF) of MCC was determined by the Kjeldahl method and sodium dodecyl sulfate (SDS)-PAGE. Sensory properties of beverages were documented by descriptive sensory analysis, and volatile sulfur compounds were evaluated using solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry. The purity of MCC measured by the Kjeldahl method (casein as a percentage of true protein) was higher after thermal treatment than before, whereas MCC purity evaluated by SDS-PAGE was unchanged by heat treatment. The purity of MCC had an effect on the flavor profile of thermally processed beverages at 6.5% protein made with fresh liquid MCC. No sulfur/eggy flavor was detected in MCC beverages when 95% of the MDWP was removed (MCC purity about 93 to 94%) from skim milk by microfiltration at 0.1, 1, and 2% fat. As the fat content of 6.5% protein beverages produced with MCC increased, sulfur/eggy flavor intensity and hydrogen sulfide concentration decreased. However, the effect of increasing milk fat on reducing sulfur/eggy flavor in MCC-based beverages at 6.5% protein was less than that of increasing MDWP removal from MCC. Sulfur off-flavors in neutral-pH dairy protein beverages can be mitigated by use of high-purity MCC or by incorporation of fat in the beverage, or both.

The effect of flash vacuum cooling on the flavor of ultrapasteurized milk

Ultrapasteurization (UP) extends the shelf life of milk. Direct steam injection (DSI) is commonly used for UP because milk is quickly heated and cooled. During this process, steam is directly injected into milk and removed by a vacuum cooler. Consumers do not prefer the flavor of DSI-UP milk compared with traditional high temperature short time (HTST) milk due to the higher cooked and eggy flavors of DSI-UP milk. The objective of this research was to characterize the effect of the vacuum cooler on the flavor of DSI-UP milk. Raw skim milk was pasteurized at 140°C for 2.3 s by DSI and homogenized at 20.7 MPa. By using a liquid sample port, steam-infused pasteurized milk was sampled after heating but before reaching the vacuum chamber. A septum was installed in the vacuum chamber to allow sampling of the removed volatiles by solid-phase microextraction (SPME) fiber followed by gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) combined with a sulfur-selective flame photometric detector. Steam-infused milk and vacuum-cooled milk diluted to the same solids contents were evaluated by descriptive sensory analysis and volatile compound analysis. The entire experiment was replicated 3 times. Milks cooled by the vacuum cooler were lower in sweet aromatic, sulfur/eggy, and cooked flavors than milk sampled before the vacuum cooler. Volatile compounds removed by the vacuum cooler included the sweet aromatic flavor contributors furaneol, maltol, furfural, sotolon, 2-heptanone, γ-dodecalactone, γ-decalactone, and δ-decalactone, as well as the cooked and sulfur/eggy contributors hydrogen sulfide and dimethyl sulfide. The vacuum cooler applied during DSI-UP of milk is effective at removing steam and cooling UP milk, but this process may also remove important flavor compounds from fluid milk.

Sensory Analysis for Cow Milk Product Development Using High Pressure Processing (HPP) in the Dairy Industry

High pressure processing (HPP) can be applied as an alternative thermal treatment of milk to maintain its natural and original sensory quality. Milk was processed at 600 MPa for 10 min or given thermal treatment at 125 °C for 4 s. Sensory evaluation of treated milk samples was conducted using the triangle and the acceptance and preference tests. The triangle test was used as a discriminative test to check whether there was a noticeable difference between both treated milk samples. The acceptance and preference test determined attributes of milk including colour, milkiness, creaminess, mouthfeel, and aftertaste based on the 5-point just-about-right (JAR) scale. In the triangle test, 89.5% of panellists were able to identify the odd sample and differentiate milk processed using high pressure from heat treatment. For the acceptance and preference test, 61% of panellists gave higher overall preference for the high pressure processed milk over heat-treated milk. The JAR evaluation showed no significant differences (p > 0.05) in all evaluated milk attributes which included milkiness, creaminess, mouthfeel, and aftertaste, with the exception of colour. Overall, high pressure processed milk scored better in terms of organoleptic properties as the penalty value for most attributes including colour, milkiness, mouthfeel, and aftertaste were lower than the penalty of heat-treated milk, except for creaminess. Therefore, to improve the acceptance and preference of high pressure processed milk, future development needs to focus on increasing creaminess of high pressure processed milk.

Children's perceptions of fluid milk with varying levels of milkfat

Schools participating in federal meal programs are limited to serving skim or low-fat (≤1%) flavored and unflavored milk. Few studies have directly addressed child perceptions and preferences for milk containing different amounts of milkfat. The objective of this study was to determine whether children can differentiate between flavored and unflavored fluid milk containing varying levels of milkfat and whether preferences for certain levels of milkfat exist. Flavored and unflavored milks containing 4 different percentages of milkfat (≤0.5, 1, 2, and 3.25%) were high-temperature, short-time processed, filled into half-gallon light-shielded milk jugs, and stored at 4°C in the dark. Milks were evaluated by children (ages 8-13 yr) following 7 d at 4°C. Acceptance testing and tetrad difference testing were conducted on flavored and unflavored milks with and without visual cues to determine if differences were driven by visual or flavor or mouthfeel cues. Child acceptance testing (n = 138 unflavored; n = 123 flavored) was conducted to evaluate liking and perception of selected attributes. Tetrad testing (n = 127 unflavored; n = 129 flavored) was conducted to determine if children could differentiate between different fat levels even in the absence of a difference in acceptance. The experiment was replicated twice. When visual cues were present, children had higher overall liking for 1% and 2% milks than skim for unflavored milk and higher liking for chocolate milks containing at least 1% milk fat than for skim. Differences in liking were driven by appearance, viscosity, and flavor. In the absence of visual cues, no differences were observed in liking or flavor or mouthfeel attributes for unflavored milk but higher liking for at least 1% milk fat in chocolate milk compared with skim was consistent with the presence of visual cues. From tetrad testing, children could visually tell a difference between all unflavored pairs except 2% versus whole milk and could not detect consistent differences between milkfat pairs in the absence of visual cues. For chocolate milk, children could tell a difference between all milk fat pairs with visual cues and could tell a difference between skim versus 2% and skim versus whole milk without visual cues. These results demonstrate that in the absence of package-related flavors, school-age children like unflavored skim milk as well as milk with higher fat content in the absence of visual cues. In contrast, appearance as well as flavor and mouthfeel attributes play a role in children's liking as well as their ability to discriminate between chocolate milks containing different amounts of fat, with chocolate milk containing at least 1% fat preferred. The sensory quality of school lunch milk is vital to child preference, and processing efforts are needed to maximize school milk sensory quality.

Ready-to-drink protein beverages: Effects of milk protein concentration and type on flavor

This study evaluated the role of protein concentration and milk protein ingredient [serum protein isolate (SPI), micellar casein concentrate (MCC), or milk protein concentrate (MPC)] on sensory properties of vanilla ready-to-drink (RTD) protein beverages. The RTD beverages were manufactured from 5 different liquid milk protein blends: 100% MCC, 100% MPC, 18:82 SPI:MCC, 50:50 SPI:MCC, and 50:50 SPI:MPC, at 2 different protein concentrations: 6.3% and 10.5% (wt/wt) protein (15 or 25 g of protein per 237 mL) with 0.5% (wt/wt) fat and 0.7% (wt/wt) lactose. Dipotassium phosphate, carrageenan, cellulose gum, sucralose, and vanilla flavor were included. Blended beverages were preheated to 60°C, homogenized (20.7 MPa), and cooled to 8°C. The beverages were then preheated to 90°C and ultrapasteurized (141°C, 3 s) by direct steam injection followed by vacuum cooling to 86°C and homogenized again (17.2 MPa first stage, 3.5 MPa second stage). Beverages were cooled to 8°C, filled into sanitized bottles, and stored at 4°C. Initial testing of RTD beverages included proximate analyses and aerobic plate count and coliform count. Volatile sulfur compounds and sensory properties were evaluated through 8-wk storage at 4°C. Astringency and sensory viscosity were higher and vanillin flavor was lower in beverages containing 10.5% protein compared with 6.3% protein, and sulfur/eggy flavor, astringency, and viscosity were higher, and sweet aromatic/vanillin flavor was lower in beverages with higher serum protein as a percentage of true protein within each protein content. Volatile compound analysis of headspace vanillin and sulfur compounds was consistent with sensory results: beverages with 50% serum protein as a percentage of true protein and 10.5% protein had the highest concentrations of sulfur volatiles and lower vanillin compared with other beverages. Sulfur volatiles and vanillin, as well as sulfur/eggy and sweet aromatic/vanillin flavors, decreased in all beverages with storage time. These results will enable manufacturers to select or optimize protein blends to better formulate RTD beverages to provide consumers with a protein beverage with high protein content and desired flavor and functional properties.

Consumer understanding of fluid milk and cheese processing and composition

Ultrafiltration and microfiltration are 2 types of membrane filtration commonly used by the dairy industry. Filtered milk products are becoming increasingly common, but there is concern that consumers unfamiliar with these processing methods may form negative uninformed perceptions of cheeses made with these milks. There are many studies that address the chemical and physical properties of cheeses made with filtered milk, but, to our knowledge, there are none that address consumer perception of these products. Similarly, ultrapasteurization is becoming more common for US dairy products. Although previous work has characterized consumer liking of ultrapasteurized milks, few have investigated understanding and perception of this process. The objective of this study was to explore consumer understanding of milk processing and constituents, particularly as it relates to milk used as an ingredient in cheese. To achieve this goal, we investigated the following 4 questions: (1) Does the average dairy product consumer understand the basic ingredients and nutrients in fluid milk and cultured dairy products? (2) Does the average dairy product consumer understand the basic processes for fluid milk and cultured dairy products? (3) Do different processes affect consumer perception or purchase intent? (4) Does explaining a process change consumer understanding of, beliefs about, and purchase intent for dairy products? Qualitative interviews (n = 54) and an online survey (n = 1,210) were conducted with dairy product consumers. Survey responses paralleled those from one-on-one interviews. The average dairy product consumer could recall key words related to dairy processing, composition, nutrients, and ingredients, but was largely unfamiliar with these subjects. Highly educated and older consumers were more likely to have a better understanding of dairy composition and nutrition, particularly lactose content of milk and Cheddar cheese and the source of fluid whey and whey protein. Processing-related descriptors (e.g., ultrapasteurized or ultrafiltered) in ingredient statements were likely to be overlooked on labels (especially for familiar products), as just 34% of dairy product consumers read the labels on dairy products often or always before purchase. The majority (>80%) of dairy product consumers were unfamiliar with ultrafiltered or microfiltered milk, but uninformed perceptions were generally positive. Consumers unfamiliar with processing methods were likely to assume those methods increase the price of a dairy product. For the majority of consumers, purchase intent for fluid milk and cultured dairy products was not affected when nonconventional processing terms such as ultrafiltered or microfiltered were included in the ingredients statement. This effect was consistent for fluid milk and Cheddar cheeses but not for cottage cheese, suggesting the possibility of product-specific effects. Providing respondents with a definition of filtration increased consumer understanding of, positive beliefs about, and purchase intent for fluid filtered milk and cheese made with filtered milk. Educating consumers through on-package labeling and other marketing messaging should be investigated for dairy products that incorporate processes such as ultrapasteurization or filtration.

Child preferences and perceptions of fluid milk in school meal programs

School meal programs in the United States feed approximately 30 million children each day and account for the majority of child milk intake. Dairy consumption during childhood and adolescence has lasting effects on lifelong health status, so it is important for schools to ensure adequate consumption in this life stage by offering an appealing product. This study identified the intrinsic and extrinsic attributes that influence children's perceptions, attitudes, and consumption of fluid milk at school, especially as they relate to fluid milk packaging. An online choice-based conjoint survey (n = 211) and four 1-h focus groups (n = 31) were conducted with child milk consumers ages 8 to 13 yr to evaluate extrinsic attributes. The survey evaluated milk package attributes including packaging type, front-of-package graphics, package color, and labeled milk fat content. Focus group topics included preferences, usability, health, taste of fluid milk, and milk consumption habits. To evaluate intrinsic properties related to packaging, 3 varieties of milk (unflavored fat-free, unflavored low-fat, and chocolate-flavored fat-free) were produced and packaged in polyethylene-coated paperboard cartons, polyethylene terephthalate (PET) bottles, and high-density polyethylene (HDPE) bottles (all 250 mL). After 10 to 13 d of storage at 4°C under dark conditions, milks were evaluated by descriptive analysis and child acceptance testing (ages 8-13 yr; n = 126, 122, and 126 for each variety, respectively). Extrinsically, package type was the most important attribute to children, but graphics, nutritional labeling, branding, package size, and overall familiarity also drove preferences. The ideal milk packaging build from the conjoint survey was an HDPE bottle with blue-colored packaging and a cow graphic, labeled as low-fat milk. Intrinsically, all varieties of milks packaged in paperboard cartons developed package-specific flavors, including refrigerator/stale and paperboard, after 10 d of storage. These off-flavors were not detected in HDPE- or PET-packaged milks. For unflavored milks, child consumers preferred the flavor of PET- or HDPE-packaged milks over cartons, regardless of milk fat content, but preferences were not distinct for chocolate-flavored milk. The results of this study demonstrate that children's liking and preference for milk are driven by both intrinsic and extrinsic factors and suggest that improvements are needed to increase acceptance of milk currently served in school meal programs.

Invited review: Maintaining and growing fluid milk consumption by children in school lunch programs in the United States

Fluid milk consumption among children has declined for decades. Adequate consumption of milk and dairy products, especially during childhood, has beneficial health outcomes for growth, development, and reduced risk of osteoporosis, hypertension, obesity, and cancer during adulthood. Satisfaction with milk flavor, perceived health benefits derived from milk, and habit are primary drivers of lifelong milk consumption. Child preferences and attitudes for milk may differ from those of adults, and as such, understanding and fulfilling the needs of children is crucial to reverse the decline in milk consumption. School meal programs make fluid milk accessible to millions of children each day; however, regulations and school lunch procurement systems in the United States sometimes make it difficult to provide novel or value-added milk products in these programs. Total consumption of all milk types in US schools declined by 14.2% from 2008 to 2017, and the percentage of children participating in the school lunch program has also declined. This decline has also been driven by declining average daily participation in the school meal program and may also reflect children's dissatisfaction with the sensory characteristics and the form of milk offered in schools. The change in form of milk offered in schools to lower fat and lower added sugar content in the United States has been driven by government-mandated school lunch calorie and fat requirements. This review describes the current milk consumption trends among children; the structure and basic requirements of the school lunch program in total and for milk; and the intrinsic, extrinsic, and environmental factors that influence child perception, preference, and consumption of fluid milk in the US school system.

High-throughput sequencing provides new insights into the roles and implications of core microbiota present in pasteurized milk

Residual microorganisms in dairy products are closely related to their quality deterioration and safety. Based on the minimum sterilization conditions required by Grade A Pasteurized Milk Ordinance, this study explored the microbiota present in milk products that were high temperature short time pasteurized at 72, 75, 80, 83, or 85 °C for 15 s, 20 s, and 30 s separately. Based on high-throughput sequencing results, 6 phyla and 18 genera were identified as dominant microbiota. Proteobacteria and Firmicutes were the maior bacteria in phyla, and each comprising more than 50%. Pseudomonas was account for more than 42% of all the genera detected in all samples. Moreover, the changes in flavor substances in pasteurized milk, including 16 free amino acids, 9 fatty acids, and 17 volatile compounds, were detected using principal component and multi factor analyses. The Pearson correlation coefficient analysis identified six bacteria genera as the core functional microbiota that significantly affected the flavor compounds and the safety and quality of pasteurized milk. Interestingly, Pseudomonas, Omithimimicrobium, Cyanobacteria and Corynebacterium had positive correlations with the flavor substances, whereas Streptococcus and Paeniclostridium had significant negative correlations with these substances. The results may help enhance the quality control of dairy products and can be used as indicators of microbial contamination of pasteurized dairy products.

Effects of heat treatment, homogenization pressure, and overprocessing on the content of furfural compounds in liquid milk

BACKGROUND

Sterilization of milk is aimed at killing the microorganisms present. There are three main sterilization methods commonly used in milk processing: high temperature and short time (HTST) pasteurization, ultrahigh pasteurization (UP), and ultrahigh temperature (UHT) sterilization. The Maillard reaction is of special interest in studying the effect of heat treatment on milk quality. Furfural compounds are one of the typical intermediates of the Maillard reaction, which have safety risks related to mutagenic and genotoxic effects. The furfural compounds content is directly related to the heat treatment intensity.

RESULTS

The furfural compounds content was measured using high-performance liquid chromatography with ultraviolet detection in 12 min. Then, 13 levels of heat treatment intensity (combinations of temperature and time) and three levels of homogenization pressure were selected to study the change of the furfural compounds content after different processing technologies in a pilot plant. The results show a higher temperature treatment can stimulate more Maillard reaction intermediates, such as hydroxymethylfurfural and furfural. A temperature regression evaluation model and content prediction models of hydroxymethylfurfural and furfural were developed to quantify the relationship between the furfural content and heat treatment with the data from the pilot plant.

CONCLUSION

Based on the temperature evaluation model, the heating temperature of three milk products was evaluated. The homogenization pressures had little effect on the furfural content in liquid milk. The emergence of the furyl methyl ketone and methylfurfural can be detected after overprocessing of the liquid milk. © 2020 Society of Chemical Industry.

The influence of automatic associations on preference for milk type

In recent decades, organic milk has been an exception to the trend of decreased fluid milk consumption in the United States. However, the reasons behind consumer preference for organic milk over conventional and other milk types are ill-defined. The objective of this study was to use an implicit association test (IAT) and primed and unprimed preference testing to determine if fluid milk consumer preferences for milk types are influenced by implicit biases and, if so, to define these biases within the context of the consumer sensory experience. Self-reported fluid milk consumers (n = 473) participated in online IAT exercises where pairwise comparisons of milk types (conventional, organic, local, pasture-raised) were measured on both positive and negative dimensions related to cow-welfare, sustainability, health, trust, safety, and quality. Latency times from IAT responses were subsequently transformed into standardized D-scores to categorize bias effect sizes. Additionally, fluid milk consumers (n = 174) participated in preference tests that compared commercial milks representing different milk types through presentations where milk type was shown (primed) or hidden (unprimed). Following preference tests, consumers were asked to explain their preferred sample using check-all-that-apply tasks. Analysis of IAT results showed that conventional milk was more associated with negative dimension descriptors compared with organic, local, and pasture-raised milks. Additionally, a positive bias in favor of organic milk was expressed when compared with pasture-raised milk offerings; however, no differences were found in pairwise comparisons of other nonconventional milk type pairings, suggesting that consumers may conflate these designations. Blinded preference testing showed that milk preferences were largely dictated by flavor, with consumers differentiating milk types based upon flavors related to packaging, pasteurization method, and feeding systems. In primed evaluations, consumers generally expressed preferences that aligned with their explicit beliefs, and flavor considerations appeared to be a secondary differentiator of preference. Based on these results, conventional milk is associated with negative implicit beliefs related to production and product quality more often than other milk types, which was reflected in IAT evaluations and primed preference tests. However, the blinded tastings suggested that conventional milk was preferred, or competitive with, other milk types based on flavor alone. Findings from this study suggest consumer differentiation and preference of milks is significantly affected by perceptions and beliefs related to milk type. In particular, conventional milk was associated with relatively few unique belief descriptions, indicating strict utilitarian consumer categorization. Organic and local milks were comparatively associated with greater care for nutrition, sustainability, animal welfare, and local farm support. These results demonstrate a need for greater education related to conventional milk offerings to dispel factors influencing negative implicit bias. Furthermore, improving product narrative via label information and alignment with locality and regionality were identified as possible opportunities for improving consumer sentiments related to conventional milk. A more thorough understanding of these attributes may reinforce stated beliefs more effectively and stave off consumer losses to plant-based alternatives that fulfill similar beliefs.

Ultra-high Temperature (UHT) Processing: Technological Significance and Updates

Background:

Background: Milk forms an integral part of the human diet from the nutritional point of view. Besides nutrition, it has also unique functional properties which are harnessed by the industry for numerous uses. Being highly perishable specific techniques are required to minimize the losses during processing and adequate preservation of this precious commodity. In the U.S. and many other parts of the world, the traditional pasteurization of milk requires a minimum heat treatment of 72ºC for 15 seconds with subsequent refrigeration. However, the advent of Ultra High Temperature (UHT) treatment of milk has added a new dimension to the marketing of liquid milk in urban as well as remote areas without the requirement of cold chain management. The distinctive feature of UHT processed milk is that it is commercially-sterile-not pasteurized and so has long shelf life at room temperature. UHT milk, also known as long-life milk, is emerging as an attractive commercial alternative offering a hygienic product of unmatched quality, which can be bought anywhere, at any time and in any quantity. The present review will discuss numerous aspects of UHT processing of milk with reference to historical significance, fundamental principle, various systems used and prerequisites, type of exchangers used, fouling and other defects in system, chemical and microbiological effect of the treatment, its effect on nutritional components, organoleptic quality of milk and the advantage and involved challenges of the process.

Conclusion:

Raw milk is easily contaminated with pathogens and microbes and hence its consumption of raw milk is associated with certain ill health effects. Therefore, heating milk before consumption is strongly suggested. Thus, UHT treatment of milk is done to ensure microbial safety and also to extend the shelf life of this highly perishable commodity. Heating milk at such a high temperature is often associated with the change of organoleptic properties like change in flavor or cooked flavor, rancidity due to microbes or acid flavor, etc. But UHT treatment does not substantially decrease the nutritional value or any other benefits of milk.

Invited review: Astringency in whey protein beverages

Astringency is the sensation of mouth drying and puckering, and it has also been described as a loss of lubrication in the mouth. Astringency is perceived as an increase in oral friction or roughness. Astringency caused by tannins and other polyphenols has been well documented and studied. Whey proteins are popular for their functional and nutritional quality, but they exhibit astringency, particularly under acidic conditions popular in high acid (pH 3.4) whey protein beverages. Acids cause astringency, but acidic protein beverages have higher astringency than acid alone. Whey proteins are able to interact with salivary proteins, which removes the lubricating saliva layer of the mouth. Whey proteins can also interact directly with epithelial tissue. These various mechanisms of astringency limit whey protein ingredient applications because astringency is undesirable to consumers. A better understanding of the causes of whey protein astringency will improve our ability to produce products that have high consumer liking and deliver excellent nutrition.