Lactose,glucose and galactose content in milk,fermented milk and lactose-free milk products

Lactose, glucose and galactose contents in milk and fermented milk products and their lactose-free alternatives, were determined. Storage of products up to the best-before dates had no effect on carbohydrate composition. Total galactose content in yoghurt, i.e., free galactose plus the galactose moiety of lactose, was 2.3–2.4 g 100 g⁻¹ (94–95% of that in milk), whereas that in Swedish soured milk and kefir was 1.9–2.0 g 100 g⁻¹ (75–79% of that in milk). Lactose levels in lactose-free milk and fermented milk products were below or close to detection limits for all products. Only small differences in total galactose content existed for the lactose-free alternatives of milk, yoghurt and filmjölk, all with average total galactose contents of 1.3–1.4 g 100 g⁻¹ (55–60% of that in milk). In contrast, lactose-free kefir had the same galactose content as milk, 2.4 g 100 g⁻¹.     

Preconcentration of yoghurt base by ultrafiltration for reduction in acid whey generation during Greek yoghurt manufacturing

The feasibility of applying ultrafiltration (UF) to concentrate a yoghurt base prior to fermentation during Greek yoghurt manufacturing was studied as a way of minimising acid whey (AW) generation. Two Greek yoghurts were prepared by concentrating a milk base through UF to 13.8% and 17.5% (w/w) (GY‐2, GY‐3). Production of GY‐3 resulted in zero AW discharge, while the GY‐2 production discharged 78% lower AW compared to the control (GY‐1). GY‐2 exhibited a hard gel structure, low syneresis, maximum viscosity properties and a high protein and fat content. Applying both, UF and straining, resulted yoghurts with required structural attributes while substantially reducing the generation of AW.     

Size classification of precipitated calcium phosphate using hydrocyclone technology for the recovery of minerals from deproteinised acid whey

Acid whey is generated during the manufacture of acidified dairy products, such as soft cheeses, acid casein ingredients and strained yoghurts. Examples of these whey‐based by‐products include Cottage cheese acid whey and Greek yoghurt acid whey. Alkalisation of acid whey at elevated temperatures (60 °C) precipitates calcium phosphate, which can be recovered and used as an ingredient. The novel application of a liquid–solid hydrocyclone in the size classification of calcium phosphate from heated and neutralised acid whey was investigated in this study. Factors influencing hydrocyclone performance were tested, and the technology was integrated into a membrane filtration‐based process for the production of milk mineral powders.     

Influence of enrofloxacin on the coagulation time and the quality parameters of goat's milk yoghurt

Three batches of yoghurts were made from goat's milk with different enrofloxacin concentrations (0, 50, 100 and 150 μg/kg). Quality parameters were analysed at 1, 7, 14 and 28 days at 5 °C. Drug residues were also quantified by HPLC. Coagulation time and most yoghurt properties remained unaffected by the presence of enrofloxacin in goat's milk. However, quality parameters were affected by the storage period. 74.9–99.2% of enrofloxacin initially added to goat's milk remained in the yoghurt throughout its entire shelf life, potentially posing a risk to consumer health. Therefore, an enrofloxacin maximum residue limit in yoghurt should be established.     

Properties of set-style skim milk yoghurt as affected by an enzymatic or Maillard reaction induced milk protein oligomerisation

Protein oligomers (2.9 × 10⁴-3.0 × 10⁵ g/mol) were introduced into yoghurt in amounts of 15-37% of the total protein by an enzymatic modification of proteins in yoghurt milk by lactoperoxidase, laccase or glucose oxidase as well as by a dry matter increase of yoghurt milk with sodium caseinate/lactose, sodium caseinate/pectin and total milk protein/lactose Maillard products. Yoghurt from enzymatically treated milk was characterised by an up to 10% lower acidity, up to 47% diminished gel strength and up to 18% decreased whey drainage than yoghurt from untreated milk. Yoghurt from protein/saccharide Maillard product enriched milk exhibited up to 4% reduced acidity, up to 27% increased acetic aldehyde content as well as up to 58% decreased whey drainage in relation to yoghurt from untreated protein/saccharide mixture enriched milk. Sensorically, yoghurt from enzymatically treated milk as well as from protein/saccharide Maillard product enriched milk was described by an even and whey-draining appearance, by a soft, homogeneous and creamy consistency as well as by a mild, less yoghurt characteristic taste and smell.This study for the first time presents an overview over the impact of novel protein oligomerisation techniques on physicochemical and sensory properties of yoghurt in regard to possible practical applications of an enzymatic as well as Maillard reaction induced oligomerisation in complex food systems.     

Production and evaluation of some physicochemical parameters of peanut milk yoghurt

The peanut milk for yoghurt production was prepared by fortifying peanut milk (∼12 g/100 g total solids) with 4 g/100 g skimmed milk powder. The final product was subjected to physicochemical analysis using cow milk yoghurt (CMY) as a control throughout the study. Peanut milk yoghurt (PMY) had higher protein content, fat, water holding capacity and lower susceptibility to Syneresis than CMY. PMY had lower lactose level (1.73 g/100 ml) compared to CMY (4.93 g/100 ml). Generally both PMY and CMY had high mineral composition and contained high amounts of essential amino acids. PMY also contained a higher proportion of unsaturated fatty acids than saturated fatty acids as compared to CMY. Therefore, in terms of fatty acid composition, PMY could be considered to be more health promoting than CMY. Sensory evaluation revealed that though PMY had better sensory texture scores than CMY, its sensory appearance, flavor and overall acceptability scores were lower than those of CMY.     

The impact of supplementing goats' milk with quinoa extract on some properties of yoghurt

This study investigated the impact of supplementing goats' milk with quinoa extracts, in the range of 5, 10 and 15 g/100 g on the milk fermentation. The properties of yoghurt produced from this milk, which include viscosity, microstructure and sensory acceptability, were assessed. The supplementation of goats' milk with quinoa extracts, particularly permeate extract, reduced the fermentation time and enhanced the viability of lactic acid bacteria. Supplementation of yoghurt with increased levels of quinoa extracts increased the apparent viscosity and changed the yoghurt protein matrix. Panellists highly accepted the yoghurt that contained quinoa permeate extract.     

The influence of vegetable puree containing carotenoids on the nutrient composition and structure of milk yoghurt

The aim of this study was to develop technology to produce a mashed pumpkin yoghurt rich in β‐carotene and to check its physicochemical properties and nutritional values. The structural and mechanical properties of the yoghurt product, as well its basic nutrient content and antioxidant activity, were studied. Yoghurt fortified with pumpkin puree has the potential to normalise the commensal intestinal microbiota and has potential as a dietary health supplement. The experimental yoghurt samples that were produced had physicochemical properties comparable to commercially produced yoghurt: the pumpkin‐supplemented samples contained 4.5% fibre, 8.5 mg/100 g vitamin C and 8.9 mg/100 g β‐carotene.     

Properties of low-fat stirred yoghurts made from high-pressure-processed skim milk

Physical properties of stirred yoghurt made from reconstituted skim milk that was high-pressure (HP)-treated at 100, 250 or 400 MPa, at 25, 70 or 90 °C, for 10 min, prior to inoculation with yoghurt cultures, were studied; portions of milk HP-treated at 25 °C were also heat-treated at 90 °C for 10 min before or after pressure treatment. Control yoghurts were made from skim milk given a heat treatment at 90 °C for 10 min. Fermentation time was not affected by treatment applied to the milk. HP treatment of skim milk at 25 °C, before or after heat treatment, gave stirred yoghurts of similar viscosities to that made from conventionally heat-treated milk. Lower viscosities were obtained when stirred yoghurts were made with milk HP-treated at elevated temperatures. A model is proposed to correlate properties of yoghurt with HP/heat-induced changes in interactions and structures of protein in the milk samples.Industrial relevanceTo meet end user expectations, the dairy industry needs to diversify its product range by tailoring specific functionalities. To meet these expectations, new processing methods such as high-pressure processing are of interest for their potential to achieve specific and/or novel functionalities and/or improve efficiencies, including reduced chemical and water use. In this paper, an investigation of the use simultaneous pressurization and heating of milk before the manufacture of stirred yoghurt is presented.     

Distribution and stability of aflatoxin M1 during production and storage of yoghurt.

Yoghurt from cow's milk artificially contaminated with aflatoxin M1 (AFM1) at levels of 0.050 and 0.100 g l(-1) was fermented to reach pHs 4.0 and 4.6. Yoghurt fermented to pH 4.6 was also used for preparing strained yoghurt. Yoghurts were stored at 4 degrees C for up to 4 weeks. Analysis of AFM1 in milk, yoghurt, strained yoghurt and yoghurt whey was carried out using immunoaffinity column extraction and liquid chromatography coupled with fluorometric detection. AFM1 levels in yoghurt samples showed a significant decrease (p < 0.01) compared with those initially added to milk. Growth of culture lactic acid bacteria was not affected in the AFM1 contaminated yoghurts, with the exception of Streptococcus thermophilus that showed a significantly (p < 0.01) lower increase in the yoghurt containing the toxin at high concentration. Following fermentation, AFM1 was significantly lower (p < 0.01) in yoghurts with pH 4.0 than in yoghurts with pH 4.6 at both contamination levels. During refrigerated storage, AFM1 was rather more stable in yoghurts with pH 4.6 than with pH 4.0. The percentage loss of the initial amount of AFM1 in milk was estimated at about 13 and 22% by the end of the fermentation, and 16 and 34% by the end of storage for yoghurts with pHs 4.6 and 4.0, respectively. The percentage distribution ratio of AFM1 in strained yoghurt/yoghurt whey of the initial toxin present in the yoghurt was about 90/10 and 87/13 for the lower and the higher contamination levels, respectively.     

Some physicochemical properties and mineral contents of stirred yoghurts containing different fruit marmalades

In this study chemical properties and mineral levels of yoghurts containing different fruit marmalades were investigated. Cherry laurel, loquat fruit and kiwi marmalade were used to make the stirred yoghurts, and the calcium, phosphorus, sodium, magnesium, manganese, iron, zinc, copper, boron, lead, nickel, molybdenum, chromium, cadmium, cobalt levels were determined by an inductively coupled plasma optical emission spectrometer (ICP–OES). The total solid, fat, ash, pH, viscosity and syneresis contents of the yoghurt samples changed between 13.85–21.02%, 2.45–2.90%, 0.82–0.94%, 4.11–4.22, 2104–2454 cP and 42.0–47.0 mL/100 g, respectively. The mean concentrations in the yoghurts of these minerals were 104.66–118.94 calcium, 95.81–112.42 phosphorus and 13.47–15.04 magnesium as mg/100 g, 235.00–254.00 iron, 429.00–453.00 zinc and 70.45–122.90 copper as μg/100 g. The recommended dietary allowance (RDA) was calculated on the basis of the intake of one yoghurt portion (125 g).     

New experimental set-up for testing microwave technology to continuously heat fouling-sensitive food products like milk concentrates

Microwave heating is an emerging alternative direct heating method to face deposit and particle formation upon heating fouling-sensitive food products. This study successfully demonstrated the implementation of a new set-up for continuous microwave heating at pilot scale (f = 2450 MHz, P = 0.6–6 kW). Reconstituted skim milk concentrate (DM = 27, 31.5 and 36 g/100 g) was heated (110–125 °C, 5 s holding time) through microwave technology and with a tubular heat exchanger in order to examine heat-related product changes and compare both technologies.The results showed significantly reduced whey protein denaturation (35–40% less β-lactoglobulin denaturation) and deposit formation (90% less fouling) of microwave heated reconstituted skim milk concentrate compared to tubular heating, whereas colour changes were insignificant for all experiments. Both methods resulted in comparable particle sizes at equal flow profiles, however, turbulent flow conditions were necessary in order to prevent elevated particle formation.Industrial relevanceMicrowave heating is a promising alternative heating method for fouling-sensitive dairy products. This study demonstrates that through short heat-uptake times gentle product handling is ensured, resulting in retained native product properties. Reduced fouling leads to extended running times, implying less and eventually shorter cleaning intervals. Moreover, compared to other direct heating methods like steam injection, no additional water/steam is added to the product. With its space-saving design and easy handling, continuous microwave heating is a rising technology with high industrial relevance.     

Colloidal aggregation induced by the reduction in pH and the synthesis of new molecular structures during the milk fermentation process

The use of different inocula in the milk‐to‐yoghurt transformation influences the kinetics of the fermentation process. The aim of this work was to study the kinetics induced by Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (Lb–St). The milk‐to‐yoghurt transformation showed no delay in the production of lactic acid for yoghurt produced using Lactobacillus johnsonii with S. thermophilus (La1–St) or Lactobacillus casei with S. thermophilus (Lc1–St); the delays were 20–70 min and 40–80 min, respectively. The absence of delay was 1.0/min (Lb–St) as compared with 0.015/min (La1–St) and 0.7/min (Lc1–St). The kinetics was fitted using second‐order reaction.     

Influence of guar gum addition on physicochemical,microbial, rheological and sensory properties of stirred yoghurt

This study investigated the effects of adding guar gum (0, 0.6 and 0.8 g/100 mL) on the physicochemical, microbial, rheological and sensory properties of stirred yoghurt. Incorporation of guar gum into the yoghurt significantly affected the pH and colour, but did not significantly influence the lactic acid bacteria counts. The magnitudes of apparent viscosity (η_a,100), consistency index (K), yield stress (σ_oc), storage modulus (G′) and loss modulus (G″) for yoghurt samples containing guar gum (0.6–0.8 g/100 mL) were significantly greater than those for the control (without guar gum), indicating that guar gum can improve the steady and dynamic shear rheological properties of yoghurt.     

The quality of set‐style yoghurt responsible to partial lactose hydrolysis followed by protein cross‐linking of the skimmed milk

Skimmed milk used for set‐style yoghurt production was treated with lactase at 0.1 g/kg for 30 min to give partial lactose hydrolysis and then treated with horseradish peroxidase and glucose oxidase at 200 and 6 kU/kg protein to result in protein cross‐linking. Two treatments conferred higher apparent viscosity on the milk, but led to the yoghurt prepared from it with insignificantly different chemical compositions to the counterparts (P > 0.05). The prepared yoghurt also showed decreased syneresis (about 17.7%), higher apparent viscosity and viscoelastic modulus, firmer texture and finer microstructure. This ternary enzyme system is a potential approach to improving the quality of set‐style yoghurt.     

Eliciting the Sensory Modalities of Fat Reformulated Yoghurt Ice Cream Using Oligosaccharides

In the present work, fat reduction of Greek strained yoghurt ice cream (YIC) was carried out in three proportional milkfat levels i.e. 30, 50 and 70% using three types of oligosaccharides namely long-chain inulin, oligofructose and maltodextrin 12 DE. Greek strained yoghurt was blended with ice cream mixes in ratios of 1:3 and 1:1. The physico-chemical, textural and thermal characteristics of the YIC mixes and their obtained frozen end products were determined. The sensory modalities (olfactory, gustatory, tactile and oro-tactile) of the YIC were monitored following 2 and 16 weeks of quiescent frozen storage at ?25 °C. Milkfat reduction impaired significantly (p?<?0.05) the perceived creaminess and mouthcoating sensation stimuli, whist it intensified the oral tissue friction associated sense stimuli such as astringency, wateriness and coarseness. Long-chain inulin- and maltodextrin-based samples received the highest scores for creaminess, mouthcoating, gumminess, hardness and iciness. The increase of the yoghurt to ice cream mix ratio escalated the friction/recrystallization-associated sensations e.g. astringency, sourness, coarseness and wateriness. Notwithstanding yoghurt supplementation reinforced the pseudoplasticity and macroviscosity of the ice cream mixes, it suppressed their aeration capacity leading to heavy-bodied ice creams. However, no significant effects of yoghurt supplementation level on the colligative and meltdown rate of the YIC formulations were identified. Partial least squares coupled discriminant analysis (PLS-DA) revealed that fat reformulation of YICs using oligosaccharides results in a substantially diversified sensory profile. Generally, a 50% fat reduction of YICs using long-chain oligosaccharides appears to be a technologically tangible solution.     

Investigating probiotic yoghurt to reduce an aflatoxin B1 biomarker among school children in eastern Kenya: Preliminary study

Aflatoxin exposure remains a health problem in developing countries. The mean concentration of aflatoxin B1 in maize meal samples from eastern Kenya of 17.4 ppb verified that the food was contaminated. A probiotic yoghurt was created containing aflatoxin B1 binding Streptococcus thermophilus, Lactobacillus rhamnosus GR-1 and Weissella cibaria NN20 isolated from fermented kimere, a dough food product made from millet. Forty primary school children, with maize being a regular part of their diet, were randomly assigned to consume 200 mL yoghurt or control milk daily for 7 days, followed by a 7 day washout and another 7 day treatment. After both 7 day treatment periods, aflatoxin metabolite 1 concentration in urine samples was significantly lower than baseline in the probiotic group (P > 0.01), but increased in the milk group. The findings were confirmed using liquid chromatography-mass spectrometry (LC–MS). This suggests that locally produced probiotic yoghurt may reduce aflatoxin poisoning in Kenyan children.     

Effect of total milk solid content adjusted by adding ultrafiltered milk retentate on quality of set mango yoghurt

The quality of set mango yoghurt prepared by varying total milk solids (TMS) level in mango yoghurt mix, by adding 5× ultrafiltered cow skim milk retentate and cow milk cream, was investigated. The water‐holding capacity (WHC) and values of textural attributes of mango yoghurt increased, whereas body and texture and overall acceptability scores decreased significantly (P < 0.05) with increasing TMS level. The optimised product (10.2% TMS level) was compared with conventional mango yoghurt. Acetaldehyde concentration, WHC, values of textural attributes, body and texture, overall acceptability scores and pH were significantly (P < 0.05) higher in optimised compared with conventional mango yoghurt.     

Volatile organic compound profiles of yoghurt produced from cow's milk with different somatic cell counts

The present study aimed to investigate the effect of somatic cell count (SCC) of raw cow's milk on the volatile organic compound (VOC) profiles of yoghurt. Test yoghurt samples were produced from three batches of cow's milk with low, medium and high SCC, respectively. The VOCs were determined by gas chromatography–mass spectrometry (GC–MS) analysis. A lower diacetyl and acetoin content and a higher content of 2‐heptanone, and butanoic and hexanoic acids were established in the yoghurt samples from batches with high SCC of above 1 000 000 cells/cm³. The increased SCC of cow's milk had a negative effect on the volatile organic compound profiles of yoghurt.