Starch addition in renneted milk gels: partitioning between curd and whey and effect on curd syneresis and gel microstructure.

Milk gels were made by renneting and acidifying skim milk containing 5 different starches, and then compressed by centrifugation to express whey and simulate curd syneresis during the manufacture of low-fat cheese. A series of 17 starches were examined, with 5 starches being selected for in-depth analysis: a modified waxy corn starch (WC), a waxy rice starch (WR), an instant tapioca starch (IT), a modified tapioca starch (MT), and dextrin (DX). Milks containing WC, WR, and DX were given a 72°C heat treatment, whereas those containing IT and MT had a 30-min treatment at 66°C that matched their optimum gelatinization treatments. Curd yields were calculated by weight, estimated starch content in whey was measured gravimetrically by alcohol precipitation, and starch retention in curd was calculated. Curd yields were 13.1% for the control milk (no added starch) and 18.4, 20.7, 21.5, 23.5, and 13.2% for the gels containing starches WC, WR, IT, MT, and DX, respectively. Estimated starch retentions in the curd were, respectively, 71, 90, 90, 21, and 1%. Laser scanning confocal microscopy was used to determine the location of the starches in the curd and their interaction with the protein matrix. Waxy corn, WR, and IT starches have potential to improve texture of low-fat cheese because they had high retention in the curd and they generated interruptions in the protein matrix network that may have helped limit extensive protein-protein interactions. Modified tapioca starch interfered with formation of the protein structure of the curd and produced a soft noncohesive gel, even though most (79%) of the MT starch was lost in the whey. Few distinct starch particles were present in the MT curd network. Dextrin was not retained in the curd and did not disrupt the protein network, making it unsuitable for use in low-fat cheese.

Survival of microencapsulated probiotic Lactobacillus paracasei LBC-1e during manufacture of Mozzarella cheese and simulated gastric digestion.

An erythromycin-resistant strain of probiotic Lactobacillus paracasei ssp. paracasei LBC-1 (LBC-1e) was added to part-skim Mozzarella cheese in alginate-microencapsulated or free form at a level of 10(8) and 10(7)cfu/g, respectively. Survival of LBC-1e and total lactic acid bacteria (LAB) was investigated through the pasta filata process of cheese making (in which the cheese curd was heated to 55 °C and stretched in 70 °C-hot brine), followed by storage at 4 °C for 6 wk and simulated gastric and intestinal digestion. This included incubation in 0.1 M and 0.01 M HCl, 0.9 M H(3)PO(4), and a simulated intestinal juice consisting of pancreatin and bile salts in a pH 7.4 phosphate buffer. Some reductions were observed in both free and encapsulated LBC-1e during heating and stretching, with encapsulated LBC-1e surviving slightly better. Changes in total LAB losses during heating and stretching did not reach statistical significance. During storage, a decrease was observed in total LAB, but no statistically significant decrease was observed in LBC-1e. Survival during gastric digestion in HCl was dependent on the extent of neutralization of HCl by the cheese, with more survival in the weaker acid, in which pH increased to 4.4 after cheese addition. The alginate microcapsules did not provide any protection against the HCl. It is interesting that survival of the encapsulated LBC-1e was greater during incubation in H(3)PO(4) than in the HCl gastric juices. Proper selection of simulated gastric digestion media is important for predicting the delivery of probiotic bacteria into the human intestinal tract. Neither free nor encapsulated LBC-1e was affected by incubation in the pancreatin-bile solution. Based on the level of probiotic bacteria in cheese needed to provide a health benefit and its survival during simulated gastric digestion, as determined in this study, it should theoretically be possible to lower the amount that needs to be ingested in cheese by up to a factor of 10(3) compared with other fermented dairy foods or when consumed as supplements.

Improvement in melting and baking properties of low-fat Mozzarella cheese.

Low-fat cheeses dehydrate too quickly when baked in a forced air convection oven, preventing proper melting on a pizza. To overcome this problem, low-fat Mozzarella cheese was developed in which fat is released onto the cheese surface during baking to prevent excessive dehydration. Low-fat Mozzarella cheese curd was made with target fat contents of 15, 30, 45, and 60 g/kg using direct acidification of the milk to pH 5.9 before renneting. The 4 portions of cheese curd were comminuted and then mixed with sufficient glucono-δ-lactone and melted butter (45, 30, 15, or 0 g/kg, respectively), then pressed into blocks to produce low-fat Mozzarella cheese with about 6% fat and pH 5.2. The cheeses were analyzed after 15, 30, 60, and 120 d of storage at 5°C for melting characteristics, texture, free oil content, dehydration performance, and stretch when baked on a pizza at 250°C for 6 min in a convection oven. Cheeses made with added butter had higher stretchability compared with the control cheese. Melting characteristics also improved in contrast to the control cheese, which remained in the form of shreds during baking and lacked proper melting. The cheeses made with added butter had higher free oil content, which correlated (R2≥0.92) to the amount of butterfat added, and less hardness and gumminess compared with the control low fat cheese.

Microstructural changes in casein supramolecules during acidification of skim milk.

Pasteurized skim milk was acidified using different levels of glucono-delta-lactone at 10, 20, 30, and 40 degrees C to give slow, medium, and fast rates of acidification. Milk coagulation was monitored by measuring turbidity and curd firmness, and microstructural changes during acidification were observed on glutaraldehyde-fixed, agar-solidified milk samples using transmission electron microscopy. Rate of acidification had little influence on changes observed during acidification, except at 10 degrees C. At 40 degrees C, the casein supramolecules were spherical throughout acidification, whereas at lower temperatures they became progressively more ragged in appearance. All of the milks gelled at the same pH (pH 4.8), as measured by curd firmness, whereas increases in turbidity, assumed to be brought about by an increase in number of light-scattering particles, were observed to start at about pH 5.2 to 5.4. As the milk was acidified, aggregates of loosely entangled proteins were observed, presumably originating from proteins that had dissociated from the casein supramolecules. These aggregates were often as large as the casein supramolecules, particularly as the pH of the milk approached the isoelectric point of the caseins. Larger aggregates were observed at 40 degrees C than at the lower temperatures, suggesting the involvement of hydrophobic interactions between the proteins. A 3-phase model for acid-induced gelation of milk is proposed in which the first phase involves temperature-dependent dissociation of proteins from the casein supramolecules, with more dissociation occurring as temperature is decreased. Dissociation continues as milk pH is lowered, with the released proteins forming into loosely entangled aggregates, some as large as the casein supramolecules. The second phase of acid gelation of milk occurs between pH 5.3 and pH 4.9 and involves a reassociation of proteins with loosely entangled protein aggregates forming into more-compact colloidal particles or combining with any remaining casein supramolecules. The third and final phase involves rapid aggregation of the colloidal casein supramolecules into a gel network at about pH 4.8. Different gel structures were formed based on temperature of acidification, with a coarse-stranded gel network formed at 40 degrees C and a fine-stranded gel network at 10 degrees C.

Hardening of high-protein nutrition bars and sugar/polyol-protein phase separation.

UNLABELLED: Use of hydrolyzed proteins is known to delay hardening of high-protein nutrition bars. Bars were formulated using ratios of 0%, 25%, 50%, 75%, or 100% partially hydrolyzed whey protein isolate (HWPI) to nonhydrolyzed whey protein isolate (WPI) in one experiment, and either WPI or HWPI combined with high-fructose corn syrup (HFCS) or sorbitol syrup (SS) in a 2nd experiment along with vegetable shortening such that initial a(w) was 0.59 for HWPI bars and 0.64 for WPI bars. After mixing, the dough was extruded into bars and stored at 32 degrees C for accelerated shelf-life testing. Hardness, color, and microstructure were measured during 42 d of storage. Bars initially had similar hardness of approximately 3.4 N that increased during storage. Bars with HWPI were softest with hardness at 37 d of 10 to 15 N compared to almost 100 N for bars with WPI. Water activity increased for WPI bars to 0.69 by 34 d. Bars became darker during storage depending on amount of Maillard browning reactants, that is, HWPI/HFCS bars >> HWPI/SS > WPI/HFCS bars > WPI/SS bars. Bar microstructure at day 2 showed protein and fat dispersed in particulate form throughout the carbohydrate syrup within the bar matrix. During storage, a single nonlipid phase developed in HWPI bars while in WPI bars a phase separation occurred between protein and carbohydrate. We propose that such phase separation initiates bar hardening and promotes subsequent protein aggregation. Successful formulation of HPN bars depends on cosolvent properties of the polyol/sugar toward the proteins and their preferential exclusion from the solvation layer surrounding the proteins. PRACTICAL APPLICATION: High-protein nutrition bars can be formulated so they remain soft during storage by selecting proteins and sugars that are compatible with each other. Otherwise, the protein and sugar will separate from each other which can then lead to hardening.

Influence of brine concentration and temperature on composition, microstructure, and yield of feta cheese.

The protein matrix of cheese undergoes changes immediately following cheesemaking in response to salting and cooling. Normally, such changes are limited by the amount of water entrapped in the cheese at the time of block formation but for brined cheeses such as feta cheese brine acts as a reservoir of additional water. Our objective was to determine the extent to which the protein matrix of cheese expands or contracts as a function of salt concentration and temperature, and whether such changes are reversible. Blocks of feta cheese made with overnight fermentation at 20 and 31 degrees C yielded cheese of pH 4.92 and pH 4.83 with 50.8 and 48.9 g/100 g of moisture, respectively. These cheeses were then cut into 100-g pieces and placed in plastic bags containing 100 g of whey brine solutions of 6.5, 8.0, and 9.5% salt, and stored at 3, 6, 10, and 22 degrees C for 10 d. After brining, cheese and whey were reweighed, whey volume measured, and cheese salt, moisture, and pH determined. A second set of cheeses were similarly placed in brine (n = 9) and stored for 10 d at 3 degrees C, followed by 10 d at 22 degrees C, followed by 10 d at 3 degrees C, or the complementary treatments starting at 22 degrees C. Cheese weight and whey volume (n = 3) were measured at 10, 20, and 30 d of brining. Cheese structure was examined using laser scanning confocal microscopy. Brining temperature had the greatest influence on cheese composition (except for salt content), cheese weight, and cheese volume. Salt-in-moisture content of the cheeses approached expected levels based on brine concentration and ratio of brine to cheese (i.e., 4.6, 5.7 and 6.7%). Brining at 3 degrees C increased cheese moisture, especially for cheese with an initial pH of 4.92, producing cheese with moisture up to 58 g/100 g. Cheese weight increased after brining at 3, 6, or 10 degrees C. Cold storage also prevented further fermentation and the pH remained constant, whereas at 22 degrees C the pH dropped as low as pH 4.1. At 3 degrees C, the cheese matrix expanded (20 to 30%), whereas at 22 degrees C there was a contraction and a 13 to 18 g/100 g loss in weight. Expansion of the protein matrix at 3 degrees C was reversed by changing to 22 degrees C. However, contraction of the protein matrix was not reversed by changing to 3 degrees C, and the cheese volume remained less than what it was initially.

Mealybug beta-proteobacterial endosymbionts contain gamma-proteobacterial symbionts.

Some insects have cultivated intimate relationships with mutualistic bacteria since their early evolutionary history. Most ancient 'primary' endosymbionts live within the cytoplasm of large, polyploid host cells of a specialized organ (bacteriome). Within their large, ovoid bacteriomes, mealybugs (Pseudococcidae) package the intracellular endosymbionts into 'mucus-filled' spheres, which surround the host cell nucleus and occupy most of the cytoplasm. The genesis of symbiotic spheres has not been determined, and they are structurally unlike eukaryotic cell vesicles. Recent molecular phylogenetic and fluorescent in situ hybridization (FISH) studies suggested that two unrelated bacterial species may share individual host cells, and that bacteria within spheres comprise these two species. Here we show that mealybug host cells do indeed harbour both beta- and gamma-subdivision Proteobacteria, but they are not co-inhabitants of the spheres. Rather, we show that the symbiotic spheres themselves are beta-proteobacterial cells. Thus, gamma-Proteobacteria live symbiotically inside beta-Proteobacteria. This is the first report, to our knowledge, of an intracellular symbiosis involving two species of bacteria.

Comparative floral development of Mir-grown and ethylene-treated, earth-grown Super Dwarf wheat.

To study plant growth in microgravity, we grew Super Dwarf wheat (Triticum aestivum L.) in the Svet growth chamber onboard the orbiting Russian space station, Mir, and in identical ground control units at the Institute of BioMedical Problems in Moscow, Russia. Seedling emergence was 56% and 73% in the two root-module compartments on Mir and 75% and 90% on earth. Growth was vigorous (produced ca. 1 kg dry mass), and individual plants produced 5 to 8 tillers on Mir compared with 3 to 5 on earth-grown controls. Upon harvest in space and return to earth, however, all inflorescences of the flight-grown plants were sterile. To ascertain if Super Dwarf wheat responded to the 1.1 to 1.7 micromoles mol-1 atmospheric levels of ethylene measured on the Mir prior to and during flowering, plants on earth were exposed to 0, 1, 3, 10, and 20 micromoles mol-1 of ethylene gas and 1200 micromoles mol-1 CO2 from 7 d after emergence to maturity. As in our Mir wheat, plant height, awn length, and the flag leaf were significantly shorter in the ethylene-exposed plants than in controls; inflorescences also exhibited 100% sterility. Scanning-electron-microscopic (SEM) examination of florets from Mir-grown and ethylene-treated, earth-grown plants showed that development ceased prior to anthesis, and the anthers did not dehisce. Laser scanning confocal microscopic (LSCM) examination of pollen grains from Mir and ethylene-treated plants on earth exhibited zero, one, and occasionally two, but rarely three nuclei; pollen produced in the absence of ethylene was always trinucleate, the normal condition. The scarcity of trinucleate pollen, abrupt cessation of floret development prior to anthesis, and excess tillering in wheat plants on Mir and in ethylene-containing atmospheres on earth build a strong case for the ethylene on Mir as the agent for the induced male sterility and other symptoms, rather than microgravity.

Silica deposition on the leaves of Mir- and Earth-grown Super Dwarf wheat.

Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) microanalysis were used to investigate the nature of crystals deposited on leaves of Mir- and Earth-grown Super Dwarf wheat (Triticum aestivum L.) plants. Leaves from these plants exhibited dense and uniformly distributed crystals on leaf abaxial surfaces when viewed by SEM. Young leaves showed that crystals initially accumulated around the stomata on the adaxial surface, but became more dense and uniformly distributed as the leaves aged. EDX microanalyses of the Balkanine (a nutrient charged clinoptilolite zeolite) medium in which the wheat plants were grown showed an elemental pattern similar to that observed on the wheat leaves. The absence of N and P in the Balkanine suggests that they were completely utilized by the plants. Only Si and O were evident in the drying agent, Sorb-it-Silica (TM), and perhaps could have accounted for some of the Si observed on the plant tissue. Grant numbers: NCC2-831, 84322-4810

Observations on toxicity to mice of rumen fluid from sheep fed roughage or concentrate diets.

Raw rumen liquor derived from sheep fed a wheat grain plus limestone diet was 2.5 times more toxic when injected into mice than liquor from sheep fed lucerne chaff. Liquors from transitional diets were of intermediate toxicity. Lactic acid was apparently not the toxic factor and relatively high molecular weight substances are implicated.

Effects of mineral buffers on the rumen flora of sheep fed grain diets.

The structure of the microbial population of rumen liquor froom sheep fed diets of roughage and of whole wheat grain with and without mineral buffer additives was studied. Addition of either 2 per cent of a mixture of 1/1/1/1 sodium bicarbonate, potassium bicarbonate, disodium hydrogen phosphate and calcium hydrogen phosphate or of 1 per cent of aluminium hydroxide to grain diets acted to increase microbial concentration, allow persistance of a rumen flora of predominatly Gramnegative staining characteristic, and to increase the proportion of rods. Animals consuming these diets had an improved production performance. In the absence of dietary buffers the microbial population shifted towards a Gram-positive population with no reduction in the proportion of coccal forms.

Microlesions on rumen papillae of sheep fed diets of wheat grain.

Scanning electron microscope evidence of microlesions on the rumen papillae of lambs fed a wheat grain diet is presented. These represent an early and previously unrecognised stage of rumenitis.