Effects of feed composition,protein denaturation and storage of milk serum protein/lactose powders on lactosylation

During whey powder production, the feed is subjected to several heat treatments which can cause lactosylation of proteins. In this study, lactosylation of whey proteins was evaluated in spray-dried powders before and after storage by varying the native protein fraction as well as the serum protein/lactose ratio in the powders. The lactosylation of native α-lactalbumin and β-lactoglobulin in the powders before storage was not affected to a large extent by the protein denaturation or if the feed had been heat treated in a high or low lactose environment. After storage (relative humidity of 23.5%, 30 °C, 25 days), the kinetic of lactosylation tended to increase with increasing native protein fraction and bulk protein content in the powders. An explanation could be that proteins dissolved in the lactose glassy structure might have a lower reactivity, while proteins present in the protein glassy structure with dissolved lactose may display higher lactosylation reactivity.     

Dietary fiber,fructooligosaccharides, and physicochemical properties of homogenized aqueous suspensions of yacon (Smallanthus sonchifolius)

Yacon roots are a promising source of inulin­type fructans (35 g/100 g dry matter) with a total amount of dietary fiber of about 45 g/100 g dry matter. The polydispersity of the particle size distribution of yacon aqueous suspension was reduced with increasing the degree of homogenization due to two phenomena: aggregation of particles, and disruption of large particles. Non­homogenized yacon suspensions exhibited large cell clusters that were disrupted into small cell clusters, single cells, and aggregates. The most concentrated suspension exhibited mainly aggregates.The volume fraction of the suspensions decreased significantly with increasing the degree of homogenization. This was attributed to a denser packing of small particles and aggregates in between large particles thus allowing the water within the structure to be released.Yacon suspensions exhibited high elastic modulus (750 Pa) at low water insoluble solids content (0.9% WIS). Additional results suggested that inulin­type fructans contributed to the elastic properties of yacon suspensions.The yacon suspensions studied in this work can be considered as semi­concentrated suspensions, i.e. the plot elastic modulus of the suspensions versus concentration exhibited a region immediately after the transition region. Particle interactions seem to be of great importance in this region in the particular case of yacon suspension since the elastic modulus (G′) reached 750 Pa at low water insoluble solids content (< 1%).     

High number of Yersinia enterocolitica 4/O:3 in cold-stored modified atmosphere-packed pig cheek meat

Yersinia enterocolitica is a psychrotrophic, facultative anaerobic zoonotic bacterium belonging to family Enterobacteriaceae and it can be transmitted from pigs to humans through pork. The growth of bacteria belonging to Enterobacteriaceae and aerobic spoilage bacteria is usually effectively restricted by 20% or more CO(2) enriched atmosphere at refrigerated temperatures. In this study, 40 samples of meat strips from pig cheek (musculus masseter) and 40 samples from hind leg (m. semimembranosus) muscles were packaged in modified atmosphere (MA) (30% CO(2)/70% O(2)) and stored at 6°C for 12d. Twenty naturally contaminated samples per muscle type were studied on days 1 and 13. Violet red bile glucose (VRBG) and de Man Rogosa Sharpe (MRS) agar plates were used for enumeration of Enterobacteriaceae including Y. enterocolitica and lactic acid bacteria, respectively. During the 12-d storage at 6°C in MA, the mean number of bacteria on pork strips of cheek meat was increasing from 1.6 to 4.5 log cfu/g and from 3.1 to 7.2 log cfu/g on VRBG and MRS agar plates, respectively. Most of the oxidase-negative isolates on VRBG plates, which were isolated from the cheek meat samples after 12-d cold storage in MA, were identified as Y. enterocolitica 4/O:3. The mean number of this pathogen was 4.1 log cfu/g varying between 2.3 and 5.4 log cfu/g. The pH of the cheek meat and leg meat was measured on days 1 and 13, and it remained high (pH>6) in most cheek meat samples during the storage. No Y. enterocolitica 4/O:3 was isolated from meat strips of hind leg. This study shows that cheek meat of slaughter pigs is contaminated with Y. enterocolitica 4/O:3 and that this pathogen can grow well on raw pork packaged in MA at 6°C even in the presence of high number of lactic acid bacteria.     

How important is tryptophan in human health?

Tryptophan (Trp) is an amino acid and an essential component of the human diet. It plays a crucial role in many metabolic functions. Clinicians can use Trp levels in the course of diagnosing various metabolic disorders and the symptoms associated with those diseases. Furthermore, supplementation with this amino acid is considered in the treatment of depression and sleep disorders, mainly due to the Trp relationship with the synthesis of serotonin (5-HT) and melatonin. It is also used in helping to resolve cognitive disorders, anxiety, or neurodegenerative diseases. Reduced secretion of serotonin is associated with autism spectrum disorder, obesity, anorexia and bulimia nervosa, and other diseases presenting peripherals symptoms. The literature strongly suggests that Trp has a significant role in the correct functionality of the brain-gut axis and immunology. This information leads to the consideration of Trp as an essential dietary component due to its role in the serotonin pathway. A reduced availability of Trp in diet and nutraceutical supplementation should be considered with greater concern than one might expect. This paper constitutes a review of the more salient aspects gleaned from the current knowledge base about the role of Trp in diseases, associated nutritional disorders, and food science, in general.     

Effects of breed and age at slaughter on degradation of muscle lipids during processing of dry‐cured hams

Hams from Landrace, Duroc and Hampshire pigs slaughtered at ages 6, 7.5 and 9 months were processed to generate Norwegian Parma‐style hams. Lipid contents and the compositions of fatty acid classes (ΣSFA, ΣMUFA, ΣPUFA) within neutral lipids, phospholipids and free fatty acids were determined. Small differences in lipid degradation and composition of the classes were revealed. However, significant sensory differences related to lipids were observed. Breed was more important than age. Dry‐cured Hampshire hams gave a more intense mature odour that may be associated with higher overall lipid degradation. Unexpectedly, these hams also demonstrated high juiciness and tenderness, which could be related to the melting characteristics of the fat. Dry‐cured Duroc hams showed a higher susceptibility towards rancidity, presumably associated with preferential oxidation of n‐6 fatty acids relative to C18:1 n‐9. Dry‐cured Landrace hams showed the lowest juiciness and tenderness, likely due to their lower fat content (marbling).     

Microbiological analysis of seed sprouts in Norway

As part of larger survey of microbial contamination of fruits and vegetables in Norway, four different sprouted seed products were analysed for bacterial and parasitic contaminants (n = 300 for bacterial analyses and n = from 17 to 171 for parasite analyses, depending on parasite). Escherichia coli O157, Salmonella, Listeria monocytogenes, Cyclospora oocysts, Ascaris eggs and other helminth parasites were not detected in any of the sprout samples. Thermotolerant coliform bacteria (TCB) were isolated from approximately 25% of the sprout samples, with the highest percentage of TCB positive samples in alfalfa sprouts. Most TCB were Enterobacter spp. and Klebsiella. E. coli was isolated from 8 of 62 TCB positive mung bean sprout samples. Cryptosporidium oocysts were detected in 8% of the sprout samples and Giardia cysts were detected in 2% of the samples. All the Cryptosporidium positive samples, and most of the Giardia positive samples, were mung bean sprouts. Parasite concentrations in positive samples were low (between 1 and 3 oocysts/cysts per 50 g sprouts). Sprout irrigation water was also analysed for microbial contaminants. E. coli O157 and L. monocytogenes were not detected. TCB were isolated from approximately 40% of the water samples. Salmonella reading was isolated from three samples of spent irrigation water on 3 consecutive days. Cryptosporidium and Giardia were also isolated from spent irrigation water. Additionally, eight samples of unsprouted mung bean seed were analysed for Cryptosporidium oocysts and Giardia cysts. One or both of these parasites were detected in six of the unsprouted seed samples at concentrations of between 1 and 5 oocysts/cysts per 100 g unsprouted seed. Whilst our results support spent irrigation water as the most suitable matrix for testing for bacteria, unsprouted seed is considered the more useful matrix for analysing for parasite contaminants.     

Overproduction of pentose phosphate pathway enzymes using a new CRE-loxP expression vector for repeated genomic integration in Saccharomyces cerevisiae

Two new vectors are described, the expression vector pB3 PGK and the CRE recombinase vector pCRE3. The pB3 PGK has a zeocin-selectable marker flanked by loxP sequences and an expression cassette consisting of the strong PGK1 promoter and the GCY1 terminator. The S. cerevisiae genes RKI1, RPE1, TAL1 and TKL1 were cloned in pB3 PGK and integrated in the locus of the respective gene, resulting in overexpression of the genes. S. cerevisiae TMB 3026, simultaneously overexpressing the RKI1, RPE1, TAL1 and TKL1 genes, was created by successive integrations and removal of the loxP-zeocin-loxP cassette using pCRE3. The 2mu-based pCRE3 carries the aureobasidin A, zeocin and URA3 markers. pCRE3 proved to be easily cured without active counter-selection. The zeocin marker is present on both the pB3 PGK and on pCRE3, so that screening for zeocin sensitivity indicates both chromosomal marker loss and loss of the pCRE3 vector. This feature saves time, since only one screening step is needed between successive chromosomal integrations. Marker recycling did not lead to increased zeocin resistance, indicating that the zeocin marker could be used for more than four rounds of transformation. The use of the CRE/loxP system proved to be a practical strategy to overexpress multiple genes without exhausting available markers.     

Passivation of the aluminium cathode during deposition of aluminium from aluminium chloride-sodium chloride melts

The kinetics of aluminium deposition from NaCl-AlCl₃ melts (c_AlCl3 < 10 mol%) contained in alumina crucibles was studied by linear sweep voltammetry and potential step amperometry at temperatures around 820°C. At low concentrations (c_AlCl3 < 0.4 mol%) the reduction of AlCl₃ on liquid aluminium has been found to be diffusion controlled. At higher concentrations a passivation of the aluminium electrode was observed during the deposition reaction. The passivation appears to be caused by precipitation of alumina from supersaturated melt in the diffusion layer at the aluminium cathode.     

Inhibition of Bacillus cereus spore outgrowth and multiplication by chitosan

Bacillus cereus is an endospore-forming bacterium able to cause food-associated illness. Different treatment processes are used in the food industry to reduce the number of spores and thereby the potential of foodborne disease. Chitosan is a polysaccharide with well-documented antibacterial activity towards vegetative cells. The activity against bacterial spores, spore germination and subsequent outgrowth and growth (the latter two events hereafter denoted (out)growth), however, is poorly documented. By using six different chitosans with defined macromolecular properties, we evaluated the effect of chitosan on Bacillus cereus spore germination and (out)growth using optical density assays and a dipicolinic acid release assay. (Out)growth was inhibited by chitosan, but germination was not. The action of chitosan was found to be concentration-dependent and also closely related to weight average molecular weight (M_w) and fraction of acetylation (F_A) of the biopolymer. Chitosans of low acetylation (F_A = 0.01 or 0.16) inhibited (out)growth more effectively than higher acetylated chitosans (F_A = 0.48). For the F_A = 0.16 chitosans with medium (56.8 kDa) and higher M_w (98.3 kDa), a better (out)growth inhibition was observed compared to low M_w (10.6 kDa) chitosan. The same trend was not evident with chitosans of 0.48 acetylation, where the difference in activity between the low (19.6 kDa) and high M_w (163.0 kDa) chitosans was only minor. In a spore test concentration corresponding to 10²-10³ CFU/ml (spore numbers relevant to food), less chitosan was needed to suppress (out)growth compared to higher spore numbers (equivalent to 10⁸ CFU/ml), as expected. No major differences in chitosan susceptibility between three different strains of B. cereus were detected. Our results contribute to a better understanding of chitosan activity towards bacterial spore germination and (out)growth.