Evaluating the effectiveness of minimum chlorate technologies employed by manufacturers of skim milk powder from both microbiological quality and chemical residue perspectives.

Dairy processors in the Republic of Ireland have adopted chlorine-free chemicals for cleaning and chlorine gas for water disinfection as a means of minimizing chlorate residue in dairy products. For these 'minimum chlorate technologies' to be satisfactory, they must be able to deliver product with acceptable levels of bacteria as well as minimum levels of chlorate and other chlorine based residues. To establish the effectiveness of these technologies, sampling was conducted across the skim milk powder (SMP) manufacturing chain in 3 separate milk processing sites. Across the 3 sites a total of 11 different batches of SMP were sampled in duplicate from the whole milk silo through the manufacturing process to the powder product; yielding a total of 137 samples. Samples were tested for chlorate, perchlorate and trichloromethane alongside a suite of microbiological plate count tests including total bacteria, thermophilic bacteria, thermoduric bacteria and both mesophilic and thermophilic spore-forming bacteria. Chlorate was detected at reportable levels (≥0.01 mg/kg) in 9 of 22 SMP samples analyzed; resulting in a mean chlorate concentration 0.0183 mg/kg. Bacteria were ubiquitous across all samples analyzed with spore-forming bacteria counts ranging from 1.30 to 2.33 log cfu/ g in SMP.

Physicochemical properties of skim milk powder dispersions prepared with calcium-chelating sodium tripolyphosphate, trisodium citrate, and sodium hexametaphosphate.

Due to health benefits of proteins, the demand for protein beverages has grown rapidly. Translucent protein drinks with neutral pH may have advantages over acidic beverages that may cause dental erosion, and skim milk powder (SMP) is an affordable protein ingredient. Dissociating casein micelles by calcium chelators is a well-known method to reduce SMP dispersion turbidity, but much is to be studied for physicochemical properties as affected by chelator type and concentration. The objective of the present study was to characterize physicochemical properties of dispersions with 5% (wt/vol) SMP after addition of 0 to 30 mM sodium tripolyphosphate, trisodium citrate, or sodium hexametaphosphate. The turbidity was decreased with increasing chelator concentration, with the lowest turbidity observed in the SMP dispersions with sodium hexametaphosphate. The smallest hydrodynamic diameter was observed at an intermediate chelator concentration, resulting from the balance of casein micelle dissociation and aggregation of dissociated caseins induced at an elevated ionic strength. Heating at 90°C for 5 min increased turbidity but lowered hydrodynamic diameter of SMP dispersions, with some exceptions. The morphology of SMP dispersions differed for each chelator and was also affected by chelator concentration and heating. Trisodium citrate was the most effective to demineralize colloidal calcium phosphate in casein micelles, but the amount of dissolved calcium was not directly correlated with the decreased turbidity, indicating different chelating mechanisms by each chelator. Analysis of serum calcium and phosphorus concentrations also suggested that the type and concentration of soluble and insoluble calcium phosphates and their partitioning in the serum and casein micelles were dynamically changed by the studied parameters to affect dispersion turbidity and structures of casein micelles. Findings from the present study may be used to formulate translucent beverages incorporating SMP and other casein micelle ingredients.

Dairy cow feeding system alters the characteristics of low-heat skim milk powder and processability of reconstituted skim milk.

Low-heat skim milk powder (LHSMP) was manufactured on 3 separate occasions in mid lactation (ML, July 4-20) and late lactation (LL, September 27 to October 7) from bulk milk of 3 spring-calving dairy herds on different feeding systems: grazing on perennial ryegrass (Lolium perenne L.) pasture (GRO), grazing on perennial ryegrass and white clover (Trifolium repens L.) pasture (GRC), and housed indoors and offered total mixed ration (TMR). The resultant powders (GRO-SMP, GRC-SMP, and TMR-SMP) were evaluated for composition and color and for the compositional, physicochemical, and processing characteristics of the reconstituted skim milk (RSM) prepared by dispersing the powders to 10% (wt/wt) in water. Feeding system significantly affected the contents of protein and lactose, the elemental composition, and the color of the LHSMP, as well as the rennet gelation properties of the RSM. The GRO and GRC powders had a higher protein content; lower levels of lactose, iodine, and selenium; and a more yellow-green color (lower a* and higher b* color coordinates) than TMR powder. On reconstitution, the GRO-RSM had higher concentrations of protein, casein, and ionic calcium, and lower concentrations of lactose and nonprotein nitrogen (% of total N). It also produced rennet gels with a higher storage modulus (G') than the corresponding TMR-RSM. These effects were observed over the combined ML and LL period but varied somewhat during the separate ML and LL periods. Otherwise, feeding system had little or no effect on proportions of individual caseins, concentration of serum casein, casein micelle size, casein hydration, heat coagulation time, or ethanol stability of the RSM at pH 6.2 to 7.2, or on the water-holding capacity, viscosity, and flow behavior of stirred yogurt prepared by starter-induced acidification of RSM. The differences in the functionality of the LHSMP may be of greater or lesser importance depending on the application and the conditions applied during the processing of the RSM.

Investigation of the use of whey powder and buttermilk powder instead of skim milk powder in yogurt production.

The aim of this study was to determine some physical, chemical, microbiological and organoleptic properties of set-type yogurts made with six different skim milk powder (SMP), whey powder (WP) and buttermilk powder (BMP) during a 21-day period. Samples were taken from yogurts on day 1, 7, 14 and 21. Analyses were carried out on the total solids, fat, non-fat solids, protein, ash, viscosity, syneresis, pH, titratable acidity values. The counts of Streptococcus salivarius subsp. thermophilus, Lactobacillus delbrueckii subsp. bulgaricus and yeasts-molds were enumerated. Also, sensory evaluations were performed at the same times. The substitution effect of WP and BMP for SMP on ash, viscosity, syneresis and titratable acidity values of yogurts were found to be significant (p < 0.05), while total solids, non-fat solids, protein contents, pH value and S. thermophilus, L. bulgaricus and yeasts-molds counts were not statistically significant. The effect of storage period on protein, ash, viscosity, and titratable acidity values, and L. bulgaricus and yeasts-mold counts was found to be significant (p < 0.05) statistically. However, it was observed that the changes of total solids, fat, non-fat solids, syneresis, pH values, and S. thermophilus counts were insignificant during the storage period. The sensory evaluations showed that sample D was most preferred by panelists.

Changes in the volatile profile of skim milk powder prepared under different processing conditions and the effect on the volatile flavor profile of model white chocolate.

The objective of this work is to determine the extent to which changes in the skim milk powder (SMP) manufacturing process alter the volatile profile of SMP, and whether these changes are carried through to a final product when the SMP is used as an ingredient and subjected to further processing. The manufacture of SMP is a multistage process involving a preliminary concentration step, heat treatment, and a drying stage. However, the methods and conditions used by the industry are not standardized, and the inherent variability in the production of SMP has consequences for the end-users, such as the confectionery industry, where the SMP is used as an ingredient during the production of milk chocolate, white chocolate, and caramel. This study investigates the effect of each stage of the manufacturing process on the concentration of reducing sugars and available amino groups (as precursors of the Maillard reaction) as well as on the volatile products of the Maillard reaction and lipid degradation. Eight types of SMP were produced using combinations of different processing conditions: concentration (by evaporation or reverse osmosis), heat treatment (low heat or high heat), and drying (spray-drying or freeze-drying). Maillard precursors were quantified after each processing stage and volatile compounds were extracted using solid-phase microextraction, and analyzed by gas chromatography-mass spectrometry. The resulting SMP were incorporated into a model white chocolate system, produced under varying conching conditions. We demonstrate not only that changes in the SMP manufacturing conditions affect the volatile profile of SMP, but also that these differences can be carried through to a final product when the SMP is used to prepare a model white chocolate. Understanding these differences is important to the industry for controlling the flavor of the end product.

Southeast Asia's import demand for skim milk powder: Implications for US exporters.

Dairy industries in Southeast Asia are small and produce less than the domestic market demands. As expenditure and population grow in Southeast Asia, it is expected that the expenditures on skim milk powder (SMP) will grow. In this study, we examined the competitiveness of US SMP in the Southeast Asian market with respect to other leading dairy exporters, including the European Union (EU-28), New Zealand, and Australia. Using monthly data from 2006 to 2015, Rotterdam models were used to estimate import demands for SMP in 4 Southeast Asian countries. In a scenario using annual averages from 2013 to 2015 as a baseline, our findings suggest that a 10% reduction in the US price of SMP would cause Indonesia, Singapore, Vietnam, and the Philippines SMP imports from the United States to increase by 3.96, 0.44, 2.68, and 1.94 kt, respectively. Under the same scenario, the value of US SMP imports would decrease for Indonesia, Vietnam, and the Philippines by $4.12, $2.93, and $2.48 million, respectively; however, the value of US SMP to Singapore would increase by $0.20 million. Singapore and Indonesia expenditures for the US SMP are elastic, which means that as expenditure and population in Southeast Asia continue to grow, a 1% increase in SMP expenditure in Singapore and Indonesia would result in 1.25 and 1.20% increases in US SMP exports.

Physicochemical properties of skim milk powders prepared with the addition of mineral chelators.

The objective of this study was to determine the effect of mineral chelator addition during skim milk powder (SMP) manufacture on the solubility, turbidity, soluble protein, and heat stability (HS). Three chelators (sodium citrate dihydrate, sodium polyphosphate, and disodium EDTA) at 3 different concentrations (5, 15, and 25mM) were added to skim milk concentrate (30% total solids), and the pH was adjusted to 6.65 before spray drying to produce SMP. Spray-dried SMP samples were tested for solubility index (SI). Additionally, samples were reconstituted to contain 9% total solids, adjusted to pH 7.0, and tested for turbidity, protein content from supernatants of ultracentrifuged samples, and HS. Lower SI values were observed for samples treated with 5mM disodium EDTA and sodium polyphosphate than control samples or samples with 5mM sodium citrate dihydrate. Furthermore, lower SI values were observed with an increased level of chelating agents regardless of chelator type. A decreased turbidity value was found with increasing levels of mineral chelating salt treatment. Low turbidity with increasing levels of added chelators may be associated with the dissociation of caseins from micelles. Furthermore, higher protein content was observed in supernatants of ultracentrifuged samples treated with increased level of chelators as compared with the control sample. Higher HS was observed in samples treated with 5mM compared with samples treated with 25mM mineral chelator. The results suggest improved solubility and HS upon addition of mineral chelators to SMP during its manufacture.

Physicochemical and sensory characteristics of fat-free goat milk yogurt with added stabilizers and skim milk powder fortification.

Goat milk yogurt has a less consistent coagulum compared with cow milk yogurt; furthermore, the presence of goat milk in foodstuffs imparts a characteristic flavor that can restrict its acceptance by consumers. This study aimed to assess and compare the physicochemical and sensory characteristics of fat-free goat milk yogurts with added stabilizers or bovine skim milk powder to improve the final product. Four treatment additions were evaluated: (1) a mixture of 0.1% (wt/vol) carrageenan and 0.1% (wt/vol) pectin (treatment CR); (2) 0.5% (wt/vol) pectin (treatment PE); (3) 4.65% (wt/vol) bovine skim milk powder (treatment BM); and (4) control (no stabilizer; treatment CT). The physicochemical parameters were investigated at on d 1 and 5 of storage. The BM treatment presented higher pH and titratable acidity values, resulting in a buffering capacity effect. The total crude protein (CP) and solids-not-fat (SNF) contents were also higher in BM compared with the other evaluated treatments because of the addition of bovine skim milk powder. We detected a reduction in pH values for all treatments. Lower SNF contents were present in the CR and CT treatments, which might be related to a syneresis process during storage; moreover, an increase in total CP was observed for all treatments due to the proteolytic action of the starter culture. Sensory attributes, including appearance (color, consistency, and presence of lumps), texture (consistency, viscosity, and presence of lumps), flavor (bitter, sweet, and characteristic of commercial plain nonfat yogurt), and overall impression were evaluated by quantitative descriptive analysis. The addition of 0.5% (wt/vol) of pectin (PE treatment) strengthened the curd; however, the visual and oral presence of lumps and a higher bitterness score were noted by trained panelists, which resulted in the lowest overall impression score for the PE treatment. In several sensory attributes, the CR treatment was considered similar to the control; the mixture of 0.1% (wt/vol) carrageenan and 0.1% (wt/vol) pectin was not as effective as expected. Goat milk yogurt containing added bovine skim milk powder (BM) had improved consistency, viscosity, and flavor due to its higher SNF and total CP contents, which are particularly important for the desirable texture of plain nonfat yogurt. In addition, the BM yogurt was considered to have characteristics most similar to that of available commercial brands and achieved the best score for overall impression.

Effect of different fat replacers on the physicochemical and instrumental analysis of low-fat cupuassu goat milk yogurts.

The aim of this Research Communication was to investigate the changes in physicochemical, colour, apparent viscosity and texture properties in low-fat goat milk yogurts prepared with cupuassu pulp by the addition of inulin (SI), maltodextrin (SM), whey protein (SW) and skim milk powder (SP). Three batches of each cupuassu goat milk yogurt were prepared and analysed on the 1st day of storage by pH, proximate composition, colour, apparent viscosity, and texture. In comparison to yogurts from whole (W) or skimmed milk (S), all of the fat replacers improved the physicochemical properties (P < 0·05). The addition of the carbohydrates (inulin and maltodextrin) and proteins (whey protein and skim milk powder) also influenced the colour of the low-fat cupuassu goat milk yogurt (P < 0·05). All fat replacer treatments (SI, SM, SW and SP) presented a higher (P < 0·05) apparent viscosity than W and S yogurts. However, only the addition of skim milk powder increased the texture parameters (firmness and consistency) (P < 0·05). These results suggest that skim milk powder can be used to improve the texture properties of low-fat cupuassu goat milk. Furthermore, inulin, maltodextrin, and whey protein can potentially be applied in the goat dairy industry to increase the viscosity of yogurts.

Egg quality and productive performance of laying hens fed different levels of skimmed milk powder added to a diet containing Lactobacillus acidophilus.

The current trial was carried out on a commercial poultry farm to study the effect of skim milk powder (SMP) added to a diet containing Lactobacillus acidophilus on performance and egg quality of laying hens from 20 to 49 wk of age. A total of 2,400 Hy-Line W-36 laying hens were housed in 600 unenriched cages (4 hens each) located over 4 tier levels. Animals were assigned to 1 of 3 experimental treatments (0, 3, and 4). The laying hens assigned to treatments 3 and 4 received a diet enriched respectively with 3 and 4% SMP, whereas the animals in treatment 0 were fed a diet without SMP. All diets, moreover, were supplemented with L. acidophilus D2/CSL. Hen performance was determined throughout the experimental period and egg quality was measured on 30 eggs per treatment every week. Results showed that productive performance in terms of egg production, egg weight, and feed conversion ratio was not influenced by SMP at 3 or 4% of the diet. Egg quality was significantly affected by SMP included at 3 or 4% of the diet. Eggs from treatments 3 and 4, in fact, displayed higher shell thickness than those from treatment 0 (P < 0.0001). Likewise, specific gravity, Haugh unit, and shell percentage were significantly affected by the addition of SMP. In conclusion, in our study, SMP added to a diet containing L. acidophilus had no significant effects on the productive parameters of hens during the laying period, whereas significant improvements were found in certain egg quality characteristics.

Non-fat milk solids attenuate hypercholesterolemic effect of conjugated linoleic acid.

The present study instigates the notion that non-fat milk has a beneficial effect on hypercholesterolemia caused by dietary conjugated linoleic acid (CLA). Two groups of mice (6 per group) were fed synthetic CLA (predominantly a mixture of t10, c12 and c9, t11 isomers) at 1 % level in the diet with or without skim milk powder (SMP). Another group (control) was fed a similar diet without CLA and SMP. The study was conducted for 60 days (d). Daily feed intake and weekly body weight were recorded. Plasma lipid profile was determined monthly. At the conclusion of experiment, animals were sacrificed and liver tissue was removed to assay cholesterol and triacylglycerols (TAG). Following 60 day feeding, the plasma total cholesterol content increased significantly in CLA group (218 mg/dl) than in control group (167 mg/dl), while in CLA + SMP group (fed non-fat milk solids along with CLA), it was similar to that in control group. The fractions of high density lipoproteins (HDL) and low density lipoprotein + very low density lipoprotein (LDL + VLDL) cholesterol as well as triacylglycerols (TAG) in plasma increased in CLA group, but in CLA + SMP group it remained similar to the control levels. Thus, it is concluded that dietary CLA increases plasma cholesterol and TAG contents in mice on normocholesterolemic diet and the inclusion of non-fat milk solids reverses this effect.

Extraction of protein from apricot kernel oil press cake (AKOPC) through innovative techniques and the formulation of supplemented yogurt.

The apricot kernel oil press cake (AKOPC) is a high protein natural by-product of oil mechanical expression with potential uses in cosmetics, medicines, and food. The purpose of this research was to improve the protein extraction process from apricot kernel oil press cake by using enzymatic extraction (EEP), aqueous extraction (AEP), and ultrasound extraction (UEP) process. Protein extraction by AEP was facilitated by a low solid-liquid ratio (SLR) (1:15.97) and prolonged reaction durations (3.30 h), resulting in extraction yields of 68%. When compared to the AEP by similar reaction time, increased enzyme utilization (0.90%) in the EEP resulted in greater protein extraction yields (70%) in a shorter reaction time. In addition to AEP and EEP, ultrasound extraction was also used to improve protein extractability. Temperature (50°C), power density (225 W/L), and extraction duration (20 min) were shown to be the best extraction points. Protein yield was found to be 56.47% at ideal UEP conditions. The experimental values for these reactions were found to be equivalent to the predicted values formed by the mathematical models. When supplementary skimmed milk powder (SMP) was substituted with apricot kernel protein (AKP) in the yogurt manufacturing process, the total solids, average titratable acidity, total protein, and fat contents of the yogurt were increased. In contrast, pH and syneresis values decreased as AKP increased in the resulting yogurt, whether fresh or after 7 days of cold storage. Substitution of additional SMP with AKP in yogurt production might be recommended up to 35%.

Influence of minerals on the foaming properties of milk.

A comprehensive study on the effect of mineral content on milk foaming properties was conducted. Samples with increased mineral concentration were prepared by adding four different types of minerals (KH2PO4, K3Cit, CaCl2 and MgCl2) at three different concentration levels (5, 10 and 20 mM) in both reconstituted skim milk powder and milk protein concentrate. Samples with reduced minerals were prepared by reconstituting milk protein concentrate in modified simulated milk ultrafiltrates. Different mineral types showed different effects on the physicochemical properties of milk samples. The addition of K3Cit increased the viscosity and decreased the surface tension while there were no significant differences between the samples added with KH2PO4, MgCl2, or CaCl2. In terms of foaming properties, the addition of CaCl2 or MgCl2 significantly increased the foam strength and stability while decreasing foamability. In contrast, the addition of K3Cit significantly decreased foam stability and foam strength while increasing foamability. It was also found that reduction in minerals in the range studied did not affect the foaming properties of milk. These results indicate that the effect of minerals on milk foaming properties depends on the type of mineral and the concentration. This provides an insight that while designing dairy-based food products, the mineral content can be manipulated to achieve the desired foaming properties.

Protein interactions during dry and wet heat pre-treatment of skim milk powder (dispersions) and their effect on the heat stability of recombined filled evaporated milk.

Skim milk powder (SMP) as well as aqueous dispersions were subjected to dry and wet heat pre-treatment, respectively, to improve the heat stability of recombined filled evaporated milk (RFEM) derived therefrom. However, microrheological analysis revealed that prolonged incubation caused detrimental effects on the heat stability of RFEM, which were thought to be due to protein interactions. SDS-PAGE results indicated that protein aggregation via non-disulfide covalent bonds occurred upon long-time dry or wet heat incubation. This was probably related to some Maillard reaction products, which is sustained by the increase in lactulose and protein carbonyl content. Considerable protein aggregation via disulfide bonds in the serum was found upon wet heat incubation at temperatures of at least 80 °C. Principal component analysis (PCA) revealed that the negative effects of overprocessing on the heat stability of RFEM were predominantly related to protein cross-linking via non-disulfide covalent bonds related to protein carbonylation.

Impact of Recombined Milk Systems on Gastrointestinal Fate of Curcumin Nanoemulsion.

Milk powder is an important ingredient in various foods and pediatric formulations. The textural and digestion properties of the formulations depend on the preheat treatment of the milk powder during manufacture. Thus, it is interesting to know how these modifications can influence on the release of fortified bioactive compounds during digestion with a milk matrix. In this study, a curcumin nanoemulsion was incorporated into milks reconstituted from low-heat, medium-heat and high-heat skim milk powders (SMPs) and the milks were subjected to semi dynamic in vitro digestion. All the recombined milk systems formed a curd under gastric conditions, which reduced the gastric emptying of protein and curcumin-loaded oil droplets. Because of the formation of heat-induced casein/whey protein complexes, the open fragmented curd formed by the high-heat-treated reconstituted powder resulted in higher protein and oil droplets emptying to the intestine and higher curcumin bioaccessibility. This study provides useful information for how protein ingredients can govern the fate of added health-promoting compounds during digestion.

Quinoa flour as a skim milk powder replacer in concentrated yogurts: Effect on their physicochemical, technological, and sensory properties.

Milk standardization with solids (i.e., nonfat milk solids, MSNF) for yogurt manufacture is traditionally achieved by the addition of skim milk powder (SMP). However, the addition of SMP to milk-based yogurt increases lactose content and decreases both protein content and gel firmness. Thus, in this work, quinoa flour (QF; 0%, 25%, 50%, 75%, and 100% w/w) was used to replace SMP in concentrated yogurt. The physicochemical, textural, and sensory properties and microstructure of the yogurt were evaluated during cold storage. Generally, protein content, water-holding capacity, and L* value decreased, while syneresis, textural attributes, and viscosity increased with increasing QF content. The substitution of high levels of QF (>25%, w/w) for SMP led to significantly shorter fermentation times, as compared to the control sample. The scanning electron microscopy observations showed significant changes in the yogurt microstructure as a consequence of QF replacement. Samples with 25% (w/w) substitution of QF and control had the highest scores in overall acceptance. According to the results, QF could be applied as an interesting raw material for concentrating the milk-based yogurt at substitution level of 25% (w/w).

Safety and quality aspects of whole and skimmed milk powders.

BACKGROUND: Nowadays, dried milk products are highly traded and consumed all over the world, so we aimed in this study to evaluate to what extent whole and skim milk powders are safe and comply with Egyptian standards. METHODS: Eighty samples of dried milk (50 whole milk powder and 30 skim milk powder) were gathered from several retailers and supermarkets for evaluation of their differing quality and safety parameters. RESULTS: The most frequent off-flavors recovered from whole milk powder samples were cooked ones and, in the case of skim milk powder samples, flat ones. Five samples of whole milk powder were of fair quality and three samples of poor quality, according to the sensory evaluation. The compositional parameters, moisture, %, fat, %, protein, %, and acidity, %, were measured as mean values of 3.90 ±0.15, 26.90 ±0.19, 25.53 ±0.27, and 0.99 ±0.03% in the examined whole milk powder samples and 3.77 ±0.08, 1.11 ±0.05, 34.62 ±0.29, and 1.22 ±0.03% in the examined skimmed milk powder samples, respectively. These results were within the range of component requirements set by the Egyptian Standard (2014; ES: 1780/2014) for dried milk products. Also, the microbiological safety of the milk powder samples was analyzed by assessment of the total viable count, total yeast and mold count, Coliforms count, Enterobacteriaceae, E. coli, C. sakazakii, Staphylococcus aureus, Salmonella, and Listeria monocytogenes. Staphylococcus aureus was the most prevalent isolate (36.00% and 6.67%) followed by Enterobacteriaceae (20.00% and 3.33%), of whole and skim milk powder, respectively. Enterobacteriaceae isolates included Enterobacter cloacae ssp. Cloacae, and Pantoea spp., which were specified by traditional biochemical tests and Vitek2 system. All Enterobacteriaceae isolated spp. were resistant to cephalothin, neomycin, tobramycin and colistin sulphate, and sensitive to chloramphenicol, gentamycin and nalidixic acid. E. coli, C. sakazakii, Salmonella, and Listeria monocytogenes couldn't be isolated from all the tested samples. By using Inductive Coupled Plasma - Mass Spectrometer (ICP-MS), we could measure lead and mercury as mean values of 0.243 ±0.069 and 0.261 ±0.052 mg/kg for whole milk powder samples at a percentage of 68.00 and 34.00%, while for the skim milk powder samples they were 0.150 ±0.037, and 0.347 ±0.110 mg/kg at a percentage of 66.67 and 40.00%, respectively. CONCLUSIONS: Finally, thirty-four whole milk powder and twelve skimmed milk powder samples didn't comply with Egyptian standards, so it is necessary for authorities to put more attention on this and regular monitor it.

Gluconic acid as a chelator to improve clarity of skim milk powder dispersions at pH 3.0.

Clear acidic protein beverages have a niche market. Acidification of skim milk powder (SMP) dispersions to pH 3.0 using citric acid (CA) lowers turbidity but the dispersion remains translucent. The present study aimed at comparing physicochemical properties of 5% w/v SMP dispersions acidified to pH 3.0 using chelating gluconic acid (GA) and CA and non-chelating hydrochloric acid. GA was the most effective in reducing the dispersion turbidity to 394 NTU at pH 3.0, which was further reduced to 248 NTU after heating at 90 °C for 2 min resulting in transparent dispersions. The better chelating ability of GA than CA was supported by the higher extent of dissolved CCP in serum phase. The aggregation of dissociated caseins was not observed for the GA treatment based on transmission electron microscopy. The findings from this study may be used to produce clear casein-based protein beverages.

Investigating the effect of powder manufacturing and reconstitution on casein micelles using asymmetric flow field-flow fractionation (AF4) and transmission electron microscopy.

Milk powders are commonly used for a variety of food products in which among others the milk proteins add to the properties of the products. Processing of milk can, depending on the processing parameters, change the size and structure of the proteins. These changes can be difficult to measure due to the polydispersity of milk components, which makes it a challenge to obtain direct information about the individual proteins. In this paper, the results from an investigation of casein micelle size,size distribution, and structure in reconstituted skim milk and the comparison with raw and pasteurized skim milk are reported. The investigation used asymmetrical flow field-flow fractionation (AF4) in combination with online UV, multi-angle light scattering (MALS), and refractive index (RI) detection and the results were confirmed by transmission electron microscopy (TEM). The results show that there is a difference in casein micelle size distribution between the differently processed milk samples. The casein micelles of the reconstituted milk were found to have a z-average radius of gyration of 72 nm and the casein micelles in the raw and pasteurized skim milk were 58 and 62 nm respectively. The AF4 and TEM data suggest that the cause of the larger casein micelle size is a layer of aggregated whey proteins associated with the casein micelles surface. Moreover, the TEM investigation showed that a larger proportion of the casein micelles are aggregated in reconstituted milk compared to raw and fresh skim milk. Investigation of the effect of reconstitution time shows that the amount of aggregated casein micelles decreases during the first 20 min of reconstitution. The results show that the AF4-method can provide detailed insights into the reconstitution process and properties of different milk samples. Hence, it can be used as a reference or validation for more indirect methods to track the reconstitution of milk powders.

A cross-cultural sensory analysis of skim powdered milk produced from pasture and non-pasture diets.

Understanding potential cross-cultural sensory differences in the perception of Irish dairy products is important for key markets such as the USA and China. As most Irish dairy products are produced from pasture derived milk, this study investigated the impact of pasture and non-pasture diets on the cross cultural sensory perception of skim milk powder (SMP) in Ireland, USA and China. SMP was produced from cows fed outdoors on ryegrass (GRS), ryegrass/white clover (CLV), and indoors on trial mixed rations (TMR). SMP samples were evaluated by Irish (n = 78), USA (n = 100) and Chinese (n = 106) consumers using an identical hedonic sensory acceptance test in Ireland, USA and China. Optimized Descriptive Profiling (ODP) was performed using trained assessors familiar with dairy products in Ireland (n = 25) and China (n = 22), and traditional descriptive analysis was undertaken by a trained panel (n = 7) in the USA. Volatile analysis was undertaken on each SMP sample. Hedonic assessment found that USA consumers preferred SMP derived from TMR, and Irish consumers preferred SMP from either GRS or CLV. Chinese consumers perceived SMP samples differently to the USA and Irish consumers, but preference was not influenced by diet. Both Irish and Chinese trained assessors found it more difficult to discern differences between GRS or CLV SMP, but could differentiate TMR SMP. Irish assessors preferred GRS and CLV SMP. Chinese and Irish assessors had different preferences for many attributes. Trained USA panelists found significant differences, exclusively associating pasture based diets with "cowy/barny" and "cardboard/wet paper" attributes and more intense "grassy/hay" attributes than in TMR SMP. The abundance of ten volatile compounds differed significantly based on diet with acetoin derived from carbohydrate metabolism at much greater abundance in TMR SMP. This study found that sensory perception and volatile profiles of SMP were influenced by diet and differences in sensory perception existed between the three cultural groups. Irish and USA sensory responses aligned with familiarity of dairy products derived from pasture and non-pasture diets, respectively, and Chinese sensory responses differed to Irish and USA responses likely reflecting their lack of familiarity with dairy products.