Particle crystallization during spray drying in humid air

A new and modified spray drying setup was arranged to produce spray-dried crystalline lactose particles. According to Williams–Landel–Ferry kinetics (WLF), it was suggested that a higher particle temperature and lower glass-transition temperature would increase the crystallization rate of the particles during the spray-drying process while still giving dry powders. The new experimental setup allowed the particle temperature to reach higher values by using an insulated drying chamber and also allowed the particle glass-transition temperature to reach lower values by maintaining a higher gas humidity with the aid of a condenser unit attached to the dryer. Modulated differential scanning calorimetry (MDSC) and moisture-induced sorption analysis were used to verify the crystallinity of the spray-dried lactose powders. These analyses showed a higher degree of crystallinity for the particles than have previously been reported in the literature. X-ray diffraction and Raman spectroscopic analyses were further used to identify different lactose anomers. The results suggest that only α-lactose anomer exists in the products as obtained from the modified spray-drying system. The micrographs from scanning electron microscopic analysis also indicated a very crystalline nature for the particles.     

Quantification of lactose using ion-pair RP-HPLC during enzymatic lactose hydrolysis of skim milk

The correct labelling of dairy foods as “lactose-free” requires a suitably sensitive and valid analytical method for the quantification of lactose in complex food matrices. Thus, an ion-pair RP-HPLC method for the simultaneous determination of lactose, glucose and galactose in original skim milk was investigated. The samples derived from an enzymatic lactose hydrolysis approach (0.5 L) using the commercial β-galactosidase Godo-YNL2. After derivatisation with p-aminobenzoic acid and sodium cyanoborohydride, the samples were injected on a RP-C₁₈ column. Tetrabutylammonium hydrogen sulphate was used as the ion-pair reagent in the eluent system. The sugars were quantified using photometric- (UV; 303 nm) and fluorescence-detection (λ_ex 313 nm, λ_em 358 nm). The overall run time was 27 min. The limits of detection (LOD) were estimated at 2 mg L⁻¹ (UV detection) and at 0.13 mg L⁻¹ (fluorescence detection). The limits of quantification were 6 mg L⁻¹ (UV detection) and 0.45 mg L⁻¹ (fluorescence detection). Thus, this analytical method is suitable for sensitive lactose quantification in milk systems of less than 10 mg L⁻¹.     

Enhanced lactose cheese milk does not guarantee calcium lactate crystals in finished cheddar cheese

Three experimental batches of Cheddar cheese were manufactured in duplicate, with standardization of the initial cheese-milk lactose content to high (5.24%), normal (4.72%, control), and low lactose (3.81%). After 35 d of aging at 4.4°C, the cheeses were subjected to temperature abuse (24 h at 21°C, unopened) and contamination (24 h at 21°C, packages opened and cheeses contaminated with crystal-containing cheese). After aging for 167 d, residual cheese lactose (0.08 to 0.43%) and l(+)-lactate concentrations (1.37 to 1.60%) were high and d(−)-lactate concentrations were low (<0.03%) for all cheeses. No significant differences in lactose concentrations were attributable to temperature abuse or contamination. No significant differences in l(+)- or d(−)-lactate concentrations were attributable to temperature abuse. However, concentrations of l(+)-lactate were significantly lower and d(−)-lactate were significantly higher in contaminated cheeses than in control cheeses, indicating inoculation (at d 35) with heterofermentative nonstarter lactic acid bacteria able to racemize l(+)-lactate to d(−)-lactate. The fact that none of the cheeses exhibited crystals after 167 d demonstrates that high cheese milk or residual lactose concentrations do not guarantee crystal formation. Contamination with nonstarter lactic acid bacteria can significantly contribute to d(−)-lactate accumulation in cheese.     

Coupling of dielectric and mechanical relaxations with glass transition and stickiness of milk solids

Dielectric and mechanical α-relaxations of milk solids with varying milk protein contents were determined by dielectric (DEA) and dynamic-mechanical (DMA) analysis, respectively. The frequency dependence of α-relaxations occurring around and above the glass transition was modeled by the Vogel-Fulcher-Tamman (VTF) relationship. The α-relaxations were governed by the amorphous lactose and shifted to higher temperatures when protein contents of milk solids were increased at all water activities, a_w. Increasing protein contents lowered the overall molecular motions of milk solid components which were shown by small changes in dielectric and mechanical properties above the glass transition. The α-relaxations were strongly frequency-dependent. At temperatures around and above the glass transition, the primary α processes were recorded and the corresponding relaxation times were determined. The temperature dependence of the relaxation times was affected by glass transition, solid composition and water. The relaxation times decreased with increasing temperature and water content as a result of thermal and water plasticization. Higher protein contents increased the relaxation times measured for milk solids. This was associated with small changes in α-relaxation characteristics and reduced powder stickiness. Data on the compositional effects on the relaxation times of milk solids were related to flow characteristics and powder stickiness around and above the glass transition.     

A novel thermostable β-galactosidase from Bacillus coagulans with excellent hydrolysis ability for lactose in whey

β-Galactosidase is one of the most important enzymes used in dairy industry. Here, a novel thermostable β-galactosidase was cloned and overexpressed from Bacillus coagulans NL01 in Escherichia coli. The phylogenetic trees were constructed using neighbor-joining methods. Phylogeny and amino acid analysis indicated that this enzyme belonged to family 42 of glycoside hydrolases. The optimal pH and temperature were, respectively, 6.0 and 55 to 60°C. The purified enzyme had a 3.5-h half-life at 60°C. Enzyme activity was enhanced by Mn²⁺. Compared with other β-galactosidases from glycoside hydrolase family 42, B. coagulans β-galactosidase exhibited excellent hydrolysis activity. The Michaelis constant (K_m) and maximum rate of enzymatic reaction (V_max) values for p-nitrophenyl-β-d-galactopyranoside and o-nitrophenyl-β-d-galactopyranoside were 1.06 mM, 19,383.60 U/mg, and 2.73 mM, 5,978.00 U/mg, respectively. More importantly, the enzyme showed lactose hydrolysis ability superior to that of the commercial enzyme. The specific enzyme activity for lactose was 27.18 U/mg. A total of 104.02 g/L lactose in whey was completely hydrolyzed in 3 h with addition of 2.38 mg of pure enzyme per gram of lactose. In view of the high price of commercial β-galactosidase, B. coagulans β-galactosidase could be a promising prototype for development of commercial enzymes aimed at lactose treatment in the dairy industry.     

An improved model of the seeded batch crystallization of glucose monohydrate from aqueous solutions

The current research has produced an accurate model of the non-nucleating seeded batch crystallization of glucose monohydrate which includes complex phenomena including crystal growth rate dispersion and the effect of the mutarotation reaction. The model is able to predict the population density of crystals in the batch as a function of particle size and batch time, n=n(L,t) as well as total glucose concentration in the mother liquor and the fraction of glucose in the α-d-glucopyranose form. A previous model of similar systems was limited by considering only systems with monosize seed crystals, and where growth rate dispersion had a negligible effect on the particle size distribution. Because of the nature of the ‘common history’ crystals that are produced by the growth of glucose monohydrate, the modifications required to the model to account for these additions to the model are remarkably simple. By predicting the full population density the model produces an accurate mass balance for the crystallization process, since the second moment of the crystal size distribution (CSD) may be calculated analytically at every point in the simulation. This enables the competitive kinetics between the rate of crystal mass deposition of α-glucose and the rate of production of α-glucose via the mutarotation reaction to be more accurately accounted for, and hence the significance of the mutarotation reaction on the crystal growth to be more accurately predicted.     

Sensory evaluations and stability determinations of goat milk containing galactooligosaccharides

The objectives of this study were to evaluate the feasibility of producing goat milk containing galactooligosaccharides (GOS) by β‐galactosidase and to determine the sensory attribute and stability of goat milk containing GOS. The results indicated that the maximum GOS obtained were approximately 13.9% of total sugars at pH 4.5 and temperature 40 °C. The sensory attribute of the obtained GOS was determined using a 5‐point hedonic scale in terms of taste, flavour, appearance and overall acceptability. There were significant increases in taste and overall acceptability of goat milk containing higher GOS concentration when compared to regular goat milk (control). Also, goat milk containing GOS presented a good stability over the acidic conditions. GOS in goat milk were also stable after the high heat treatment and shelf life conditions.     

Influence of calcium and phosphorus, lactose, and salt-to-moisture ratio on Cheddar cheese quality: manufacture and composition

Eight Cheddar cheeses with 2 levels of calcium (Ca) and phosphorus (P), residual lactose, and salt-to-moisture ratio (S/M) were manufactured. All cheeses were made using a stirred-curd procedure and were replicated 3 times. Treatments with a high level of Ca and P were produced by setting the milk and drawing the whey at a higher pH (6.6 and 6.3, respectively) compared with the treatments with a low level of Ca and P (pH of 6.2 and 5.7, respectively). The lactose content in the cheeses was varied by adding lactose (2.5% by weight of milk) to the milk for high lactose cheeses, and washing the curd for low lactose cheeses. The difference in S/M was obtained by dividing the curds into halves, weighing each half, and salting at 3.5 and 2.25% of the weight of the curd for high and low S/M, respectively. All cheeses were salted at a pH of 5.4. Modifications in cheese-making protocols produced cheeses with desired differences in Ca and P, residual lactose, and S/M. Average Ca and P in the high Ca and P cheeses was 0.68 and 0.48%, respectively, vs. 0.53 and 0.41% for the low Ca and P cheeses. Average lactose content of the high lactose treatments at d 1 was 1.48% compared with 0.30% for the low lactose treatments. The S/M for the high and low S/M cheeses was 6.68 and 4.77%, respectively. Mean moisture, fat, and protein content of the cheeses ranged from 32.07 to 37.57%, 33.32 to 35.93%, and 24.46 to 26.40%, respectively. The moisture content differed among the treatments, whereas fat and protein content on dry basis was similar.     

低乳糖牛奶生产工艺参数的研究

针对乳糖酶缺乏者的乳糖不耐受问题，研究如何生产乳糖水解率为60％以上的低乳糖牛奶。通过38，20，6℃不同水解温度，0．5，0．8，1．0，1．5g／kgN同乳糖酶添加量，不同作用时间等因素的单因素试验，确定了制作低乳糖牛奶的工艺参数。     

Milk powders ageing: effect on physical and functional properties

Milk powders are now considered as food ingredients, mainly because of the functional properties of milk proteins. During the storage of milk powders, many physicochemical damages, mainly dependent on lactose glass transition occur. They have important consequences on physical (flowability) and functional properties (solubility, emulsifying, and foaming properties) of milk powders. First, lactose crystallization modifies the microstructure and chemical composition of the surface of powder particles. Thus, milk powders flowability is decreased. Since the structure of milk proteins is destabilized, its solubility is damaged. Moreover, particle collapse and caking occur and mainly decrease the physical properties of milk powders (density and flowability). The mechanical stresses involved may also enhance proteins unfolding, which is detrimental to solubility. Finally, molecular mobility is favored upon ageing, and both chemical (Maillard reaction) and enzymatic reactions occur. Maillard reaction and oxidation enhance protein interactions and aggregations, which mainly lessen milk powders solubility. Maillard reaction also decreases emulsifying and foaming properties. Storage temperature and relative humidity have been considered as the predominant factors involved, but time, milk components, and their physical state also have been implied.