Invited review: Redefining raw milk quality—Evaluation of raw milk microbiological parameters to ensure high-quality processed dairy products

Raw milk typically has little bacterial contamination as it leaves the udder of the animal; however, through a variety of pathways, it can become contaminated with bacteria originating from environmental sources, the cow herself, and contact with contaminated equipment. Although the types of bacteria found in raw milk are very diverse, select groups are particularly important from the perspective of finished product quality. In particular, psychrophilic and psychrotolerant bacteria that grow quickly at low temperatures (e.g., species in the genus Pseudomonas and the family Enterobacteriaceae) and produce heat-stable enzymes, and sporeforming bacteria that survive processing hurdles in spore form, are the 2 primary groups of bacteria related to effects on processed dairy products. Understanding factors leading to the presence of these important bacterial groups in raw milk is key to reducing their influence on processed dairy product quality. Here we examine the raw milk microbiological parameters used in the contemporary dairy industry for their utility in identifying raw milk supplies that will perform well in processed dairy products. We further recommend the use of a single microbiological indicator of raw milk quality, namely the total bacteria count, and call for the development of a whole-farm approach to raw milk quality that will use data-driven, risk-based tools integrated across the continuum from production to processing and shelf-life to ensure continuous improvement in dairy product quality.     

Effect of β-cyclodextrin addition on quality of precooked vacuum packed potatoes

The usefulness of β-cyclodextrin (β-CD) in enhancing the food and nutritional quality of precooked potatoes was studied. After blanching, potato slices (Solanum tuberosum var. Agata) were cooled. This was followed by dipping in solutions containing β-CD, ascorbic and citric acids, either alone or in combination with β-CD, and vacuum packaging in pouches. The potatoes were pasteurised/precooked and cooled. These samples were then analyzed for colour parameters, microbial count, Resistant Starch (RS) concentration, fat content after a frying test immediately and after 7, 14 and 28 days of storage at 4 °C. Results showed that dipping with β-CD gave the lightest colour (ΔL*) and a more attractive appearance. However, growth of aerobic mesophilic bacteria was observed in samples dipping in solutions with β-CD alone. From the nutritional point of view, the effect of β-CD on the RS content of potatoes may be related to storage time.     

Effect of high-pressure treatment of ewe raw milk curd at 200 and 300 MPa on characteristics of Hispánico cheese

Hispánico cheese is a semihard variety made from a mixture of cow and ewe milks. Production of ewe milk declines in summer and autumn. To surmount the seasonal shortage of ewe milk and prevent the inactivation of milk enzymes by pasteurization, curd made in spring from ewe raw milk was pressurized at 200 and 300 MPa and stored frozen for 4 mo. Thawed ewe milk curds were added to fresh curd made from pasteurized cow milk for the manufacture of experimental Hispánico cheeses. Control cheese was made from a mixture of pasteurized cow and ewe milk in the same proportions as those used for experimental cheeses. Experimental cheeses exhibited lower dry matter content, higher aminopeptidase activity and total free amino acid concentration, and higher levels of acetic and propionic acids, aldehydes, alcohols, and esters compared with control cheese. In contrast, the concentration of total free fatty acids and ketones and the levels of textural parameters were significantly higher in control cheese. The use of ewe raw milk curd pressurized at 200 and 300 MPa, stored frozen and thawed for Hispánico cheese manufacture, was generally beneficial for cheese characteristics and increased cheese yield because of the lower dry matter content of experimental cheeses.     

Effect of κ-carrageenan on milk protein polysaccharide mixtures

The effect of κ-carrageenan (0, 0.025, 0.05%) on phase separation between polysaccharides (0.36% of locust bean gum (LBG), guar gum, or xanthan gum) and milk proteins (from 10.5% skim milk powder) in solution was studied. Xanthan gum was seen to be the most incompatible with milk proteins, followed by guar gum and LBG. Casein micelles were more incompatible with all polysaccharides than whey proteins. Whereas at either concentration κ-carrageenan inhibited visual phase separation, it was seen by transmission electron microscopy that samples with κ-carrageenan showed microscopic phase separation. Samples with 0.05% κ-carrageenan and either LBG or guar gum and all samples with xanthan gum could be described rheologically as weak gels, while those with no or 0.025% κ-carrageenan and either LBG or guar gum could be described as concentrated solutions. Thus, no correlation was seen between the inhibition of macroscopic phase separation by κ-carrageenan and the formation of a weak gel in solution.     

Effect of heat treatments on stability of β-lactams in milk

The presence of residues of antimicrobial substances in milk may have serious toxicological and technical consequences. To date, few studies have been done to evaluate the effect of heat treatments on β-lactam residues in milk. However, the few studies that have been conducted estimate losses of antimicrobial activity under different combinations of temperature and time using microbiological methods. The aims of this study were to calculate the kinetic parameters for the degradation of β-lactam antibiotics in milk and to develop prediction models to estimate the concentration losses of these compounds in conventional dairy heat treatments. To do so, we employed a quantitative HPLC method to calculate losses in concentrations of 10 β-lactam antibiotics in milk with different combinations of temperature and time. Increasing the temperature from 60°C to 100°C decreased the half-life of amoxicillin (372 to 50 min), ampicillin (741 to 26 min), cloxacillin (367 to 46 min), and penicillin G (382 to 43 min). These increases in temperature caused further degradation in cephalosporins, which was accompanied by a decrease in half-life times to reach very low values; for instance, 4, 5, and 6 min for cefoperazone, cephurexime, and cephapirin, respectively. Kinetic equations were applied to different heat treatments used in dairy processing. Heat treatments at high temperatures and long times (e.g., 120°C for 20 min) led to a further degradation of β-lactam antibiotics with percentages close to 100% for cefoperazone and cefuroxime. In contrast, when milk was subjected to heat treatments at lower temperatures and times (e.g., 72°C for 15 s), the degradation of β-lactam in milk did not exceed 1% for the 10 antibiotics tested.     

A comparison of the effects of storage of raw milk at 2°C and 6°C on the yield and quality of Cheddar cheese

The advantages of storing raw milk, which is to be used for Cheddar cheese manufacture, at 2°C rather than at 6°C was examined. Storage of milk at the lower temperature effectively reduced the level of psychrotroph growth, and after 4 days the psychrotroph counts in samples stored at 2°C were 100-fold lower than those found in samples stored at 6°C. There was no advantage in terms of cheese yield in storing milks at the lower temperature, but an overall improvement in cheese quality was noted in samples produced from milk stored at 2°C.     

Inactivation behavior of Pseudomonas aeruginosa by supercritical N₂O compared to supercritical CO₂

Interest is growing for a non-thermal sterilization technique in the food and pharmaceutical industries in order to ensure microbiological safety without the deterioration of product quality. In this study, supercritical nitrous oxide (SC N₂O) treatment was carried out in a multi-batch system to examine its bactericidal effect and characteristics, which largely remains unclear. The effect of operating pressure, temperature, mixing intensity, and working volume ratio (defined as the ratio of sample volume to the reactor volume to be filled with SC fluids) on the inactivation efficiency of SC N₂O were investigated in comparison with supercritical carbon dioxide (SC CO₂) treatment. Pseudomonas aeruginosa was chosen as a model microorganism. A 8-log reduction of P. aeruginosa cell concentration (10% working volume) in neutral phosphate-buffered saline was achieved by the SC N₂O treatment accompanying no pH change in the presence of vigorous mixing (600 rpm) within 6 min, in a condition of 37 °C and 10 MPa and its overall efficiency is comparable to the SC CO₂ treatment. Among the reaction parameters investigated in this study, mixing intensity appeared to be the most important operating parameter affecting the bactericidal efficiency.The release of intracellular substances in cells as a result of the SC N₂O treatment was explained as one of major bactericidal actions by the SC N₂O treatment. At the same time, relatively negligible change of proteins or enzyme activities in the cells in case of the SC N₂O treatment was observed compared to the SC CO₂ treatment. Also, the observation by scanning and transmission electron microscopy shows the milder morphological change of SC N₂O-treated cells in comparison with the SC CO₂-treated cells. This study suggests that the SC N₂O bactericidal application on food products would be a viable option over SC CO₂ application, when mild change of enzyme activity and the proteins, or no pH change are desired.     

Effect of β-carotene supplementation to prepartum Holstein cows on colostrum quality and calf performance

β-Carotene, a pro-vitamin A carotenoid, acts as an antioxidant, able to scavenge free radicals to prevent oxidative damage. It has also been shown to increase rumen microbial production in vitro. When supplemented prepartum, β-carotene increased colostral fat and protein concentrations. The objective of this experiment was to evaluate the effects of supplementing 700 mg/d β-carotene (BC) daily for 4 wk prepartum on cow performance, colostrum, and performance in subsequent calves. Eighteen multiparous Holstein cows housed in a tiestall barn were blocked by expected calving date and randomly assigned to treatments at 4 wk prepartum. Blood samples were collected 3 times a week for analysis of nonesterified fatty acids, ketones, β-carotene, and IgG. Urine samples were also collected 3 times a week for analysis of creatinine and purine derivatives. Colostrum was collected within 90 min after parturition. Calves were removed from their dams before suckling, weighed within 30 min of birth, and received 4 L of maternal colostrum. Blood samples were collected from calves before colostrum administration (0 h) and at 24 h via jugular venipuncture for analysis of IgG concentration and apparent efficiency of IgG absorption. The 18 calves born were blocked based on treatments of dams. All calves were fed 449 g/d dry matter of milk replacer (20% crude protein, 20% fat) and an 18% crude protein textured starter and water ad libitum at 2 d of age until weaning at 42 d. There were no differences in any blood parameters of cows during the prepartum period. Supplemental BC increased the solids content of colostrum compared with control (22.89% control; 27.75% BC). Calves born from control fed cows had greater efficiency of IgG absorption than those born from BC supplemented cows (52.16% control; 39.50%, BC). Calves born from BC fed cows had greater feed efficiency (average daily gain/dry matter intake) compared with those born from control supplemented cows (0.33 for control; 0.44 for BC). These data indicate that although supplementing β-carotene to cows in the prepartum period negatively affects apparent efficiency of IgG absorption, it improved feed efficiency in calves.     

Effect of Iberian×Duroc genotype on dry-cured loin quality

Dry-cured loins from three different pig genotypes were studied: GEN1: ♂ Iberian × ♀ Duroc1, GEN2: ♂ Duroc1 × ♀ Iberian; GEN3: ♂ Duroc2 × ♀ Iberian. GEN1 and GEN2 are reciprocal crosses, while the difference between GEN2 and GEN3 is the Duroc sire line. The genotype of pigs Duroc1 was selected for the manufacture of dry-cured meat products, while the genotype Duroc2 was selected for meat production. The chemical composition of the dry-cured loins was significantly different, especially the intramuscular fat (IMF) content which was highest in GEN2. Dry-cured loins from GEN3 showed lower CIE a^∗ and chroma values. IMF from GEN2 was more saturated whereas GEN3 had higher percentages of PUFA and MUFA. Loins from GEN3 had higher TBA-RS values (p > 0.05) and hexanal contents. Loins from GEN3 had higher Warner–Bratzler shear force (p > 0.05) and instrumental hardness than those from GEN2, being intermediate in GEN1. Panellists considered that loins from GEN2 were more marbled, more odorous, juicier, sweeter and less salty than loins from GEN3. Therefore, loins from GEN2 had the best quality, followed by GEN1, while GEN3 had the worst quality.     

Effect of γ-irradiation on the sensory quality of moist beef biltong

Moist beef biltong (mean moisture content = 46.7% and a_w = 0.919) was vacuum packaged and irradiated to target doses of 0, 2, 4, 6, and 8 kGy. Thiobarbituric acid reactive substance (TBARS) measurements and sensory difference and hedonic tests were performed to determine the effect of γ-irradiation on the sensory quality of the biltong. TBARS values only increased significantly (P < 0.05) if biltong was irradiated to at least 8 kGy, indicating a low degree of lipid oxidation. This can be attributed to the low fat content (on average 1.53%) of the biltong used in this study, as well as irradiation under vacuum conditions. All irradiated samples could be discriminated (P < 0.05) from non-irradiated biltong, but none was rated as less acceptable. Dissipation of volatiles before tasting (by exposing the product to aerobic conditions before consumption), a low degree of lipid oxidation and liking of distinct ‘irradiation flavours’ possibly all attributed to the flavour of irradiated biltong not being regarded as unacceptable compared to controls. Biltong irradiated at 2 and 4 kGy was however liked significantly more (P < 0.05) than other samples, indicating that slight, non-oxidative irradiation-induced flavour changes may contribute to flavour development in the usually more bland moist beef biltong. Although lean moist beef biltong can thus be irradiated to doses up to 8 kGy without adversely affecting the sensory acceptability, low dose irradiation (4 kGy) is most feasible to optimise the sensory quality.     

Effects of surface heterogeneity on the adsorption of CO₂ in microporous carbons

Carbon capture combined with utilization and storage has the potential to serve as a near-term option for CO(2) emissions reduction. CO(2) capture by carbon-based sorbents and CO(2) storage in geologic formations such as coal and shale both require a thorough understanding of the CO(2) adsorption properties in microporous carbon-based materials. Complex pore structures for natural organic materials, such as coal and gas shale, in addition to general carbon-based porous materials are modeled as a collection of independent, noninterconnected, functionalized graphitic slit pores with surface heterogeneities. Electronic structure calculations coupled with van der Waals-inclusive corrections have been performed to investigate the electronic properties of functionalized graphitic surfaces. With Bader charge analysis, electronic structure calculations can provide the initial framework comprising both the geometry and corresponding charge information required to carry out statistical modeling. Grand canonical Monte Carlo simulations were carried out to determine the adsorption isotherms for a given adsorbent-adsorbate interaction at temperature/pressure conditions relevant to carbon capture applications to focus on the effect of the surface functionalities. On the basis of the current work, oxygen-containing functional groups were predicted to enhance CO(2) adsorption in microporous carbon materials in the absence of water vapor, and the hydrated graphite was found to hinder CO(2) adsorption.     

Effect of antibacterial treatments and natural chemicals on the quality and safety of marinated raw crab paste during storage at −20°C

The effects of antibacterial treatments and several natural chemicals on the quality and safety of crab paste during storage at −20°C were investigated. All antibacterial treatments significantly reduced the bacterial total viable count (TVC) of swimming crabs, with sodium hypochlorite (NaClO) combined with ultrasonic cleaning having the best effects. Four chemicals significantly inhibited the increase in TVC, pH, and the accumulation of total volatile basic nitrogen (TVB-N) compared to controls, and their combined treatment had synergistic effects. The L ₉(3 ⁴) orthogonal experiment showed that the optimum combination was A₁B₃C₃D₂ (i.e., 0.1 g kg⁻¹ nisin, 0.4 g kg⁻¹ ε-polylysine hydrochloride, 0.3 g kg⁻¹ tea polyphenol, and 0.5 g kg⁻¹ citric acid). The TVC, TVB-N concentration, and pH in A₁B₃C₃D₃-treated samples remained far below the maximum acceptable limit for good-quality marinated, raw, aquatic animal product after 12 months of frozen storage at −20°C. Furthermore, the combined treatment (A₁B₃C₃D₃) significantly inhibited the reproduction of foodborne pathogenic bacteria and spoilage bacteria. The antibacterial treatments and natural chemicals reduced foodborne pathogenic bacteria and inhibited microbial spoilage, and therefore maintained the quality and safety of crab paste during frozen storage. Antibacterial treatments and natural chemicals could be commercially utilized to maintain the quality and safety of crab paste.     

Influence of high-temperature steam on the reactivity of CaO sorbent for CO₂ capture

Calcium looping is a high-temperature CO(2) capture technology applicable to the postcombustion capture of CO(2) from power station flue gas, or integrated with fuel conversion in precombustion CO(2) capture schemes. The capture technology uses solid CaO sorbent derived from natural limestone and takes advantage of the reversible reaction between CaO and CO(2) to form CaCO(3); that is, to achieve the separation of CO(2) from flue or fuel gas, and produce a pure stream of CO(2) suitable for geological storage. An important characteristic of the sorbent, affecting the cost-efficiency of this technology, is the decay in reactivity of the sorbent over multiple CO(2) capture-and-release cycles. This work reports on the influence of high-temperature steam, which will be present in flue (about 5-10%) and fuel (～20%) gases, on the reactivity of CaO sorbent derived from four natural limestones. A significant increase in the reactivity of these sorbents was found for 30 cycles in the presence of steam (from 1-20%). Steam influences the sorbent reactivity in two ways. Steam present during calcination promotes sintering that produces a sorbent morphology with most of the pore volume associated with larger pores of ～50 nm in diameter, and which appears to be relatively more stable than the pore structure that evolves when no steam is present. The presence of steam during carbonation reduces the diffusion resistance during carbonation. We observed a synergistic effect, i.e., the highest reactivity was observed when steam was present for both calcination and carbonation.     

Effect of probiotic co-cultures on physico-chemical and biochemical properties of small ruminants’ fermented milk

Small ruminants' fermented probiotic milk is an alternative to fermented cows' milk, especially because of the monounsaturated/polyunsaturated fatty acid profiles. The technological and biochemical potential of Bifidobacterium and Lactobacillus co-cultures, with or without inulin, on goats' and ewes' milk was assessed. Microbial stability, lactose consumption, organic acid production, proteolytic parameters and conjugated linoleic acid (CLA) production in situ, were followed in ewes' and goats’ fermented milk (EFM and GFM, respectively) over 21 days at 4 °C; technological feasibility for probiotic fermented milk production was shown. In EFM, all co-cultures presented high viable cell numbers (>7.0 log cfu mL⁻¹) throughout storage, presenting faster acidification capacities and higher CLA isomer levels than in GFM. Inulin had no impact on probiotic growth, yet contributed to storage stability. CLA isomers and proteolysis indices were co-culture dependent traits: for example, co-culture of Bifidobacterium animalis B94 with Lactobacillus acidophilus L10 registered the best CLA-production in GFM.     

Effect of high pressure processing on rheological and structural properties of milk–gelatin mixtures

There is an increasing demand to tailor the functional properties of mixed biopolymer systems that find application in dairy food products. The effect of static high pressure processing (HPP), up to 600 MPa for 15 min at room temperature, on milk–gelatin mixtures with different solid concentrations (5%, 10%, 15% and 20% w/w milk solid and 0.6% w/w gelatin) was investigated. The viscosity remarkably increased in mixtures prepared with high milk solid concentration (15% and 20% w/w) following HPP at 300 MPa, whereas HPP at 600 MPa caused a decline in viscosity. This was due to ruptured aggregates and phase separation as confirmed by confocal laser scanning microscopy. Molecular bonding of the milk–gelatin mixtures due to HPP was shown by Fourier-transform infrared spectra, particularly within the regions of 1610–1690 and 1480–1575 cm⁻¹, which reflect the vibrational bands of amide I and amide II, respectively.     

Ex vivo digestion of raw,pasteurised and homogenised milk – Effects on lipolysis and proteolysis

This study investigated the impact of pasteurisation and homogenisation on ex vivo gastrointestinal digestion of proteins and fat in bovine milk. Milk that was homogenised at 150 bar showed the highest degree of lipolysis (78%) after 120 min duodenal digestion. In comparison, milk homogenised at 50 bar showed 56% release of fatty acids whereas raw and pasteurised milk showed 49% and 44% hydrolysis, respectively. Pasteurisation had very much less effect upon lipolysis and proteolysis. Homogenisation increased the gastric proteolysis of specifically β-lactoglobulin, and also of α-lactalbumin. However, after 5 min duodenal digestion all the proteins were degraded in all milks tested. Thus, both lipolysis and proteolysis were increased by homogenisation of the milk, making fatty acids from lipids and peptides from β-lactoglobulin more readily available to the human body.     

Effect of heating on the distribution of transforming growth factor-��2 in bovine milk

The objective of this study was to characterize the impact of heat treatments on the distribution of transforming growth factor-beta (TGF-??2) between cream and skim milk and between the casein and whey fractions of skim milk. Skimming removed 45% and 62% of the TGF-??2 from raw and pasteurized milks and only 8% of the total TGF-??2 in skimmed pasteurized milk was found in whey, compared to 37% in whey from raw skimmed milk. The TGF-??2 content of whey decreased as the heat treatment of the milk increased in intensity (thermization > pasteurization > UHT sterilization). Using milk held for 1 or 2 min at temperatures ranging from 57 to 84 °C, it was shown that TGF-??2 in the whey portion decreases at temperatures above 66 °C and becomes undetectable at temperatures higher than 76 °C. Altogether, these data on the heat-induced changes in TGF-??2 content of cream, skim milk, casein and whey reveal a potentially negative impact of certain heat treatments in developing TGF-??2-enriched fractions from milk.     

Effect of irradiation on Salmonella survival and quality of 2 varieties of whole green onions

Abstract: Two varieties of green onions, Banner and Baja Verde, were inoculated with a cocktail of 3 Salmonella strains using dip and spot inoculation and irradiated at 0, 0.3, 0.6, 0.9, and 1.2 kGy using electron beam. Salmonella survivors were enumerated using a XLD underlay/TSAYE overlay plating method. The D values were in the range of 0.26 to 0.32 kGy depending on variety but not on the method of inoculation. This indicated that a 5‐log reduction of Salmonella can be achieved at a dose of 1.6 kGy. For the quality study, both varieties of green onions were irradiated at 0, 1.5, 2.0, and 2.5 kGy and evaluated for changes in microbial counts, color, texture, and visual quality during storage at 4 °C. Irradiation reduced total plate counts and psychrotrophs by 3 logs. Although the counts increased during storage, they did not exceed the initial counts of control. No significant difference was observed in color and texture between irradiated samples and control. The control maintained good visual quality for about 13 d as compared to 15 d for 1.5 and 2.5 kGy samples. The 2.0 kGy samples maintained good visual quality for 17 d suggesting that irradiation can increase shelf life by reducing spoilage microorganisms but higher doses can be detrimental to quality. At the dose levels required to achieve a 5‐log reduction in Salmonella, the shelf life of whole green onion can be extended. This study shows that irradiation can be used to enhance safety without adverse effects on quality.     

Effect of γ-irradiation on physical quality attributes and identification properties of different sauces

Gamma-irradiated (0, 1, and 10 kGy) ketchup (KTP), barbeque sauce (BBQ), and sweet chili sauce (SWC) were identified using photostimulated-luminescence (PSL) and thermoluminescence (TL) analysis and characterized for physical properties like Brix, consistency, and color. PSL-based screening showed negative results for all nonirradiated samples, while intermediated results were found for irradiated samples. Routine density separation method for mineral extraction provided better TL results; however, alkaline and acid hydrolysis could ease the process with acceptable results. A slight decrease in consistency of all the samples was observed. Brix of KTP remained unchanged, while increase of same was obvious in BBQ and SWC following irradiation. The Hunter L* value of the γ-irradiated sauces decreased except SWC samples, and the a* and b* values showed a general increase compared to the non-irradiated samples. The studied methods have potential to successfully identify and characterize the irradiated sauces for technical and regulatory requirements.