The effects of washing and chlorine dioxide gas on survival and attachment of Escherichia coli O157: H7 to green pepper surfaces

The effects of washing and chlorine dioxide (ClO₂) gas treatment on survivability and attachment of Escherichia coli O157: H7 C7927 to uninjured and injured green pepper surfaces were investigated using scanning electron microscopy and colony enumeration methods. Escherichia coli O157: H7 preferentially attached to coarse and porous intact surfaces and injured surfaces. The bacterial attachment to injured green pepper surfaces may be determined mainly by the hydrophilic properties of the injured surfaces and might not be assisted by the exocellular polymers of the bacteria. Injuries to the wax layer, the cuticle and underlying tissues increased bacterial adhesion, growth, and resistance to washing and disinfecting treatments. No significant growth of E. coli O157: H7 was found on uninjured surfaces after inoculation and incubation for 24 h at 37°C, whereas significant growth and multiplication were found on injured surfaces (P<0·05). ClO₂gas treatment was more effective as a disinfecting method than water washing. Using a membrane-plating method for resuscitation and enumeration of ClO₂-treated E. coli O157: H7 on surface-injured green peppers, 3·03±0·02 and 6·45 ±0·02 log reductions were obtained after treatments by 0·62 and 1·24 mg l⁻¹ClO₂, respectively, for 30 min at 22°C and 90–95% relative humidity. In contrast, water washing achieved log reductions of 1·5±0·05–1·67±0·10 on injured surfaces and 2·44±0·04 on uninjured surfaces.     

Selection of starters for a traditional Turkish yayik butter made from yoghurt

Butter is produced from two different materials in Turkey, cream and yoghurt. The butter produced from fresh yoghurt or ‘tulum yoghurt’ (a strained yoghurt produced from cow, goat or sheep milk) is called ‘yayik butter’ and has been traditionally produced in Turkey for centuries. In this research, we attempted to isolate and identify the natural lactic acid bacteria (LAB) of yayik butter and to select the best LAB combination for butter production. Twenty samples of yayik butter were collected from Afyon, Antalya, Isparta and Konya regions in Turkey and determined to have a mean pH of 4·78±0·33, a mean titratable acidity (lactic acid) of 0·23±0·07% and a mean NaCl of 0·55±1·22%. The mean counts of LAB (log₁₀ cfu g⁻¹) were 2·66±0·84 and 1·72±0·82 on MRS agar at 30 and 42°C, 2·44±0·93 and 1·78±0·24 on M17 agar at 30 and 42°C, and 1·64±1·196 on Sodium Azide Leuconostoc agar at 21°C, respectively. Eighty-five different LAB isolates were obtained from 20 yayik butters and identified asStreptococcus salivarius ssp. thermophilus (21·2%), Streptococcus sp. (4·7%), Lactobacillus delbrueckii ssp. bulgaricus (20%), Lactobacillus casei ssp.casei (15·3%), Lactobacillus paracasei ssp. paracasei (2·3%),Enterococcus faecium (18·8%). Leuconostoc pseudomesenteroides (Leucono-stoc mesenteroides ssp. dextranicum) (7·1%), Leuconostoc gelidum (Leuconostoc mesenteroides ssp.mesenteroides ) (4·7%) and Weissella paramesenteroides (Leuconostoc paramesenteroides) (5·9%). Combinations of S. salivarius ssp. thermophilus S51, Lb. delbrueckii ssp.bulgaricus A42, Lb. casei ssp. casei K64, Lb. paracasei ssp. paracasei A27, andLeu. pseudomesenteroides E83 were used as starter bacteria for experimental butter production from cream. Six different groups of butters were produced using different combinations of these bacteria (B, C, D and E samples), commercial culture (F sample), and without culture (A sample). Sensory evaluations showed that the experimentally produced butter sample of group B was more acceptable than the other butters. In addition, the buttermilk of sample B had lowest fact content. LAB counts of experimental butters produced with combined cultures and commercial culture were similar (6·66±1·87–6·83±0·040 and 6·81±0·13 log₁₀ cfu g⁻¹ on MRS agar, respectively).     

Aflatoxins and their Metabolites in the Tissues,Faeces and Urine from Lambs Feeding on an Aflatoxin-Contaminated Diet

Twenty-four lambs were intoxicated with 2·5 mg of aflatoxin (AF) kg^-1 in their feed for 21 days. Twelve lambs were slaughtered at day 21 and the remaining animals had an 8 day clearance period. Aflatoxins and their metabolites were detected in liver, kidneys, faeces and urine using TLC and fluorescence densitometry. During the intoxication period, the samples gave a wide range of concentrations, the lower extreme being in the liver and the kidney (0·03 μg kg^-1 of AFG₁) and the higher extreme in faeces (61·82 μg kg^-1 of AFM₁) and urine (27·84 μg litre^-1 of AFM₁). The average value of AFB₁ (1·94±0·9 μg kg^-1) was higher than AFM₁ (0·35±0·17 μg kg^-1) in the liver. In the kidney AFM₁ (5·45±4·01 μg kg^-1) was higher than AFB₁ (1·29±0·84 μg kg^-1). There were higher concentrations of AFM₁ (27·2±16·1 μg kg^-1, 7·37±6·53 μg litre^-1, respectively, of average level) in faeces and urine, than of AFB₁ (17·25±8·1 and 1·78±1·57 μg litre^-1, respectively). AFB_2a appeared in the kidney (0·05±0·03 μg kg^-1) and urine (0·35±0·25 μg litre^-1). The clearance time of AFB₁ from the faeces was less than or equal to 8 days and in all samples aflatoxin residues were still detected on the 8th day of the clearance period although in low quantities. These results suggest that aflatoxin transfer to and elimination by the liver and the renal tissue is small and that the danger to humans consuming lamb meat is also small. The examination of the faeces and urine could be useful as markers to detect lambs consuming a contaminated diet. © 1997 SCI.     

Efficacy optimization of plasma-activated water for food sanitization through two reactor design configurations

The chemistry, antimicrobial efficacy and energy consumption of plasma-activated water (PAW) was optimized by altering the discharge frequency, ground-electrode configuration, gas flow rate and initial water conductivity for two reactor configurations, i.e., air pin-to-liquid discharge and air plasma-bubble discharge in water. The ratio of NO₂⁻ and NO₃⁻ formation was altered to optimise the antimicrobial effects of PAW, tested against two Gram-negative bacteria. An initial solution conductivity of 0.2 S·m⁻¹ and 2000-Hz discharge frequency with the ground electrode positioned inside the pin reactor showed the highest antimicrobial effect resulting in a 3.99 ± 0.13-log₁₀ reduction within 300 s against Escherichia coli and 5.90 ± 0.24-log₁₀ reduction within 240 s for Salmonella Typhimurium. An excellent energy efficiency of reactive oxygen and nitrogen species (RONS) generation of 10.1 ± 0.1 g·kW⁻¹·h⁻¹ was achieved.Industrial relevancePlasma-activated water (PAW) is deemed as an eco-friendly alternative to chemical disinfection because its bactericidal activity is temporary. Optimizing the design and operation of PAW reactors to achieve high inactivation rates of more than 5-log₁₀ reductions, as demonstrated in this work, will support the industrial application of this technology and the scaleup at industrial level.     

Kinetic studies on strawberry anthocyanin hydrolysis by a thermostable anthocyanin-β-glycosidase from Aspergillus niger

Several kinetic characteristics of a thermostable anthocyanin-β-glycosidase from Aspergillus niger have been evaluated. With strawberry anthocyanins as substrate, at pH optimum (4·0) and t = 30°C, K_m was found to be $\text{123 ± 4 μ}\text{m}$ and V_max, 1·16 ± 0·06 μmol min^?1mg^?1 protein. Temperature optimum was observed at about 68°C. The apparent energy of activation was calculated to be 11 ± 1 kcal/mol. The inhibitory effect of different sugars and sugar derivatives was examined. Glucono-deltalactone ($\text{K}{}_{\mathrm{<mtext>i</mtext>}}\text{= 2·3 ± 0·1 μ}\text{m}$), gluconic acid ($\text{K}{}_{\mathrm{<mtext>i</mtext>}}\text{= 82 ± 2 μ}\text{m}$) and glucose ($\text{K}{}_{\mathrm{<mtext>i</mtext>}}\text{= 1·3 ± 0·1}\text{m}\text{m}$) appeared to be competitive inhibitors of this enzyme.     

The potential application of plant essential oils as natural food preservatives in soft cheese

Investigations were carried out to assess the efficiency of four plant essential oils; bay, clove, cinnamon and thyme as natural food preservatives. The effect of the plant essential oils at concentrations of 0·1, 0·5 and 1% was studied in low-fat and full-fat soft cheese against Listeria monocytogenes and Salmonella enteritidis at 4° and 10°C respectively, over a 14-day period. The composition of the cheese was shown to be an important factor in determining the effectiveness of the plant essential oils. In the low-fat cheese, all four oils at 1% reduced L. monocytogenes to ≤1·0 log₁₀cfu ml⁻¹. In contrast, in the full-fat cheese, oil of clove was the only oil to achieve this reduction. Oil of thyme proved ineffective against S. enteritidis in the full-fat cheese, yet was equally as effective as the other three oils in the low-fat cheese, reducing S. enteritidis to ≤1·0 log₁₀cfu ml⁻¹from day 4 onwards. It is concluded that selected plant essential oils can act as potent inhibitors of L. monocytogenes and S. enteritidis in a food product.     

Occurrence of Listeria species in raw milk in farms on the outskirts of Mexico city

Listerosis may be transmitted by direct contact with infected animals or by consumption of contaminated vegetables or meat and milk products. In Mexico, raw milk is widely consumed and the incidence of milkborne disease is unknown. A total of 1300 raw milk samples were obtained from 20 l bulk tanks at four different dairy farms in southeast of Mexico City from June 1998 to June 1999. The samples were enriched for 48 h at 30°C and plated onto McBride's Modified Agar (MMA). Suspect colonies were biochemically tested to confirm identity. Overall, 23% of all raw milk samples examined tested positive forListeria species; 13% were positive for L. monocytogenes (45·6% were serotype-4b and 54·4% were serotype 1); 6% for L. ivanovii; 4% for L. seeligeri and 1% forL. innocua. L. monocytogenes contamination was more frequent during the spring and summer months as isolation rates were 12·2% from June to October 1998 and 17% from March to June 1999. Serotype-4b isolates were not pathogenic for the mouse, while for serotype-1, strains DL₅₀ranged from 1·8×10⁶to 4×10⁷CFU ml⁻¹. Additional studies are needed to assess the public health impact of contaminated milk in Mexico.     

Some studies on the proteins of Carica papaya seeds

Protein isolates and seed meals made from Carica papaya seeds were studied with respect to their composition and functional properties. Studies showed that the seed proteins are most soluble in 5% NaCl (23·77 ± 0·15%). In all concentrations of NaCl tested, the protein has a solubility peak at pH 8·0. Classification of the protein showed that globulins constitute the bulk of the protein (53·9 ± 0·89%). The amino acid pattern of the samples studied is not too different from other plant protein sources. However, the seed appeared deficient in many amino acids.Electrophoretic studies showed that the water extract had only one band with a molecular mass of about 70·7 × 10³ daltons. The 5% NaCl extract gave five bands, with molecular mass ranging from 37·6 to 105·9 × 10³ daltons while the NaOH-soluble fraction gave six bands with a range of 18·2 to 104·0 × 10³ daltons.Compared to soya bean meal and protein concentrate, the papaya products were inferior in terms of functional properties.     

Urea and Heat Unfolding of Cold-Adapted Atlantic Cod(Gadusmorhua)Trypsin and Bovine Trypsin

The reversible unfolding reactions for phenylmethylsulphonyl fluoride (PMSF)-modified trypins from Atlantic cod (cod PMS-trypsin) and cattle (bovine PMS-trypsin) were monitored by fluorescence spectrophotometry as a function of urea concentration and temperature. For urea unfolding at 25°C, the free energy change at zero concentration of urea (ΔG(H₂O)) for cod PMS-trypsin was 11(±4·4) kJ mol⁻¹ compared with 18(±1·14) kJ mol⁻¹ for bovine PMS-trypsin, while the mid-point concentration for urea unfolding curve ([urea]_1/2) was 3·0(±0·57) M and 4·1(±0·16) M, respectively. From studies of enzyme heat unfolding, the mid point temperature of the thermal unfolding curve ( T _m ) was 46(±1·4)°C for cod PMS-trypsin compared with 57(±2)°C for bovine PMS-trypsin. The standard free energy change (Δ G° ) for reversible thermal unfolding of cod PMS-trypsin was 9(±1) kJ mol⁻¹ compared with 19(±1) kJ mol⁻¹ for bovine PMS-trypsin. Values for the enthalpy (Δ H _m ), entropy (Δ S _m ) and heat capacity (Δ C _p ) for heat unfolding are compared. Results from urea and thermal unfolding studies show that cod PMS-trypsin has a significantly lower conformational stability than bovine PMS-trypsin.     

Feeding and growth of Acrotelsa collaris (Fabricius) (Thysanura,Lepismatidae) on different types of paper

Specimens of Acrotelsa collaris were confined on representative paper samples and on filter paper impregnated with milk food. Each stadium was divisible into a feeding and a non-feeding period. Stadial and feeding durations (42 ± 1 and 29 ± 1 days) were not statistically different on the untreated papers except one. On the milk food paper stadial and feeding durations were significantly shorter (27 ± 2 and 18 ± 2 days). However non-feeding periods were not significantly different (12·0 ± 0·5 days). The total amounts of the different papers ingested in a single feeding period were similar. Art and milk food paper were eaten faster. The approximate digestibility values were in the range 63–77 per cent. There was a general loss in body weight, except on milk food paper that was replaced periodically.     

Postruminal protein supply upregulates hepatic lysine oxidation and ornithine transcarbamoylase in lactating dairy cattle

Metabolizable protein supply is a limiting factor for milk production in dairy cows, and the availability of AA is a function of the quantity of the metabolizable protein available and of hepatic AA catabolism. This study aimed to evaluate the effect of postruminal protein infusion on key genes for ureagenesis and AA catabolism. Six multiparous Holstein cows in early lactation were used in a replicated crossover design. Cows were fed a TMR and infused postruminally with either 0 or 600 g/d of milk protein isolate. Periods were 21 d long, consisting of 14 d of adjustment to surroundings, followed by 7 d of protein infusion. On the last day of each infusion, liver samples were collected for mRNA analysis and explant culture, milk samples were collected for mRNA analysis, and blood samples were collected for plasma metabolite analysis. Postruminal infusion of protein increased milk yield by 10.5%, milk fat yield by 12.5%, milk protein yield by 20%, milk lactose yield by 11%, and total solids yield by 15.5%. Postruminal infusion of protein increased milk urea N by 23.5%, blood urea N by 18.6%, and the abundance of hepatic ornithine transcarbamoylase mRNA by 52.8%. Postruminal infusion of protein did not alter the mRNA abundance of hepatic argininosuccinate synthase, α-aminoadipate semialdehyde synthase, cysteine sulfinic acid decarboxylase, or cystathionase. The abundance of RNA for milk proteins was unchanged with postruminal protein infusion. Metabolism of l-[U ¹⁴C] Lys to CO₂ was increased by 127% (0.143 vs. 0.063 ± 0.04 nmol product·mg tissue^?1·h^?1), and the metabolism of l-[U ¹⁴C] Ala to CO₂ increased by 40.5% (0.52 vs. 0.37 ± 0.06 nmol product·mg tissue^?1·h^?1) with postruminal protein infusion. The rate of l-[1-¹⁴C] Met oxidation did not differ. These data indicate increased ureagenesis matched by upregulation of nonessential AA catabolism and a disproportional increase in Lys oxidation in response to increased postruminal protein infusion.     

An attempt to produce low fat cephalotyre (Ras) cheese of acceptable quality

Two trials were carried out to produce low fat Ras cheese with acceptable organoleptic properties. In the first trial, cheese milk containing 1%, 1·5% or 2% fat and including CMC or carrageenan at levels of 0·1% and 0·02%, respectively, was used in cheese making. Control cheese was also made from milk containing 4% fat. Cheese without added stabilizers and containing lower fat levels than the control cheese had a flat flavour and tough rubbery body throughout ripening. The addition of both stabilizers improved the body characteristics of low fat cheese but did not affect flavour development in cheeses made from 1% and 1·5% fat milk and only slightly enhanced flavour intensity in cheese made from 2% fat milk.In the second trial, cheese milk of 1% or 1·5% fat with added 0·02% carrageenan was used for the preparation of Ras cheese curd. The resultant curd was then mixed with 2% of a starter culture containing S. diacetylactis and L. casei with 10 ml of 0·05% MnCl₂ solution for each kilogram of curd or reduced glutathione at a level of 100 mg/kg curd. The additives enhanced flavour intensity, improved body characteristics and accelerated the formation of both soluble nitrogenous compounds and Free Volatile Fatty Acids.     

Effects of Silage Fermentation and Post-ruminal Casein Supplementation in Lactating Dairy Cows: 1—Diet Digestion and Milk Production

Two silages were prepared from the first-cut sward of timothy-meadow fescue and wilted to a dry matter (DM) content of 300 g kg^-1. One was ensiled with the addition of a formic-acid-based additive (4 litres formic acid (FA) per tonne) and the other with the addition of a bacterial inoculant (LAB) at a rate of 5×10⁶ colony forming units g^-1. Both silages were well preserved, but the extent of fermentation was greater in LAB-silage than in FA-silage as indicated by a lower concentration of water soluble carbohydrates (68 vs 177 g kg^-1 DM) and a higher concentration of lactic acid (147 vs 32 g kg^-1 DM). Four Ayrshire cows were used in a 4×4 Latin square experiment with 21-day periods to study the effects of silage fermentation and postruminal casein supplementation on silage intake, nutrient supply and milk production. The four treatments were FA-silage without casein (FA-0), LAB-silage without casein (LAB-0), FA-silage with casein (FA-C) and LAB-silage with casein (LAB-C). Both silages were given ad libitum with 8 kg day^-1 of barley without or with 400 g day^-1 of casein infused into the duodenum. Organic matter digestibility was lower (0·723 vs 0·753; P<0·01) for FA-silage than for LAB-silage. Cows offered FA-silage had a higher molar proportion of acetate and a lower proportion of propionate in ruminal fluid than cows offered LAB-silage. Microbial protein synthesis estimated from the output of purine derivatives in urine was greater (288 vs 260 g N day^-1; P<0·05) for cows given FA-silage compared with LAB-silage. Feeding LAB-treated silage tended (P<0·10) to decrease silage DM intake compared with FA-treated silage (10·61 vs 11·77 kg DM day^-1). Silage composition did not affect significantly milk yield or milk composition. Casein infusion increased milk yield (25·1 vs 27·1 kg day^-1; P<0·05), milk protein content (32·4 vs 33·8 g kg^-1; P<0·05) and protein yield (808 vs 905 g day^-1; P<0·01). The responses were similar for both silages. © 1997 SCI.     

Dietary manipulation of the yield and composition of milk: Effects of dietary inclusions of barley and oats in untreated or formaldehyde-treated forms on milk fatty acid composition

Eight 1st-lactation cows were given four dietary treatments in a duplicated 4×4 Latin square experiment. Diets consisted of hay and soya bean meal together with barley, formaldehyde-treated barley, oats or formaldehydetreated oats (approximately 34:12:54 on a dry matter basis). Barley diets supplied 211 g fatty acids d^?1, oats diets supplied 537 g d^?1. The fatty acid composition (g kg^?1 total fatty acids) for barley diets was: 300 (16:0); 20 (18:0); 150 (18:1); 470 (18:2); 60 (18:3). Corresponding values for oats diets were 180, 20, 390, 380 and 30 g kg^?1. Formaldehyde treatment of the cereals tended to increase milk yield and reduce milk fat content (P<0·01 for barley) but did not affect milk fatty acid composition. Feeding oats in replacement for barley significantly (P<0·05) increased milk yield and lactose yield and reduced milk fat content (P<0·05 for the untreated cereals) and protein contents (P<0·01) without significant effects on milk fat or protein yields. Oats diets led to significant (P<0·001) reductions in the content of 8:0–16:0 fatty acids in milk fat with associated increases (P<0·001) in the content of 18:0 and 18:1. Changes in milk fat content of 18:2 and 18:3 acids were small. The results show the inclusion of oats in the cow's diet to be a means of reducing the saturated fatty acid content of milk fat thereby improving the nutritional value of milk and milk products and their appeal to the health-conscious consumer.     

Effects of ingredients on the characteristics of rice cakes

Steamed leavened rice cakes made from rice flour, sugar, water, yeast or baking powder were used to study the effects of ingredients on cereal-based cakes. Volume expansion linearly correlates to amylopectin and negatively correlates to amylose content (r²=0·84), with an optimum amylose/amylopectin ratio of approximately 1: 8. Higher amylopectin content resulted in sticky, elastic and unacceptable cake. The optimum water content for volume expansion was in the range of 90±5% by weight of rice flour. Sugar content correlates linearly with volume expansion and tenderness of chemically leavened rice cakes (CLRC) (r²=0·99 and 0·92, respectively). Sugar content above 50% of rice flour weight decreased volume and softness of yeast-leavened rice cakes (YLRC). Tenderness of YLRC correlates linearly to fat content (r²=0·98), but volume expansions correlates negatively to the square root of fat content (r²=0·81 and 0·97 for the two rice cakes). Both tenderness (r²>0·92) and volume expansion (r²>0·93) correlates linearly with emulsifier content up to 3% by weight of rice flour, above which the cake becomes crumbly. A little salt increased hardness, but further increase reduced both volume expansion and hardness of rice cakes. Skimmed milk powder greatly increased the expansion of CLRC. Ovalbumin content correlates linearly to volume expansion of YLRC (r²=0·87) but negatively to the expansion of CLRC (r²=0·96). The proteins that improved the textures of rice cakes were skimmed milk and egg white with an optimum content of 2–4%. Egg yolk, soya protein, whey powder and wheat gluten reduced both tenderness and volume expansion. The effects of the various ingredients interacting together were studied and the optimum formulations was determined using a Random Centroid Optimisation Program. © 1998 SCI.     

Survival of Escherichia coli O157:H7 in dried beef powder as affected by water activity,sodium chloride content and temperature

A study was carried out to determine the rate of inactivation of Escherichia coli O157:H7 in beef powder as affected by a_w(0·34±0·06±0·01), sodium chloride content (0·5, 3·0 and 20%) and temperature (5 and 25° C) over an 8-week storage time. Retention of viability of acid-adapted, acid-shocked, and control cells was determined. Overall, there were no significant differences (P≤0·05) in survival among the three types of cells subjected to the same test parameters, suggesting that mechanisms associated with induction of acid adaptation or acid shock do not result in cross protection against dehydration or osmotic stresses. At each a_wand within cell type, an increase in sodium chloride concentration resulted in significant reductions in the number of viable cells after a given storage time. Regardless of cell type, survival was significantly higher in beef powder containing 0·5 or 3% sodium chloride compared to powder containing 20% salt. The rate of inactivation was enhanced at a_w0·34±0·06 compared to a_w0·68±0·01 and at 25° C compared to 5° C.     

Greenhouse gas emission analysis for USA fluid milk processing plants: Processing,packaging, and distribution

A gate-to-gate life cycle assessment was conducted to evaluate the Global Warming Potential associated with USA fluid milk processing. Data collected from 50 fluid milk processing plants were used to construct a life cycle assessment model for the greenhouse gas (GHG) emissions across the milk processing system, from raw milk entering the plant’s refrigerated storage silo through delivery of packaged fluid milk to retail store’s loading dock. Carbon dioxide equivalent (CO₂e) emissions associated with the processing, packaging, and distribution in the processing of packaged fluid milk were investigated. Upstream emissions associated with raw materials, extraction, and transportation were included. Average GHG emissions for processing, packaging and distribution were 0.077, 0.054 and 0.072 kg CO₂e kg⁻¹ packaged fluid milk, respectively. Overall GHG emissions were 0.203 (±0.017) kg CO₂e kg⁻¹ packaged fluid milk with major individual GHG contributors being plant electricity usage (27% of total) and truck fleet tailpipe emissions (29% of total).     

Increase in low molecular size uronic acid in ripening banana fruit

Uronic acid soluble in ethanol/water (4:1 v/v) increased from 9 ± 1 mg kg^?1 fresh weight in pulp of unripe banana fruit. Musa (AAA Group, Cavendish subgroup) ‘Williams’, to 53 ± 13 mg kg^?1 fresh weight in fruit ripened for 13 days. This increase began within the first 2 days of ripening. Uronic acid soluble in phenol/acetic acid/water (2:1:1 w/v/v) increased from 15 ± 5 to 86 ± 17 mg kg^?1 fresh weight during the first 8 days of ripening, accompanied by a decrease in cell wall uronic acid from 10·2 ± 0·8 to 4·4 ± 0·4 g kg^?1 fresh weight. Most or all of the uronic acid in extracts of ripe pulp cochromatographed with monogalacturonic acid. The results were consistent with hydrolysis of cell wall polyuronides by exopolygalacturonase (EC 3.2.1.67).     

Effects of intraruminal infusions of propionate and butyrate with two different protein supplements on milk production and blood metabolites in dairy cows receiving grass silage-based diet

Four cows were used in a balanced 4×4 Latin square with 2 week experimental periods to investigate the effects of intraruminal infusions of volatile fatty acids and protein source on milk production and blood metabolites. The four treatments in a 2×2 factorial arrangement were isoenergetic intraruminal infusions of propionate (500 g day⁻¹) or butyrate (417 g day⁻¹) each given with isonitrogenous protein supplementation of fish meal (FM) or barley protein (BP). The cows were fed restrictively with 9 kg dry matter day⁻¹ of formic acid treated grass silage and 8 kg day⁻¹ of concentrate. Propionate infusion increased milk yield (24·9 vs 23·4 kg day⁻¹; P<0·05), milk protein yield (832 vs 778 g day⁻¹; P=0·05) and milk lactose content (44·7 vs 43·5 g kg⁻¹; P<0·05) and yield (1113 vs 1023 g day⁻¹; P<0·01), whereas butyrate infusion was associated with a higher milk fat content (44·7 vs 39·4 g kg⁻¹; P<0·01) and yield (1033 vs 974 g day⁻¹; P<0·01). FM tended (P<0·10) to increase milk yield, but had no significant effects on milk composition or milk component yields compared with BP. Butyrate infusion increased blood ketones, plasma non-esterified fatty acids and glycine relative to propionate infusion. The concentrations of ammonia N in rumen fluid and urea in plasma and milk were similar for both protein supplements. The profile of amino acids in plasma was similar for both protein supplements except for the higher concentrations of phenylalanine, proline and tyrosine with BP. The results show that protein utilisation can be improved by increasing the supply of propionate from rumen fermentation in cows given a grass silage-based diet. © 1998 SCI.     

Sensitivity of multidrug-resistant Salmonella typhimurium DT104 to organic acids and thermal inactivation in liquid egg products

A mixture of four Salmonella typhimurium DT104 strains and a mixture of four S. typhimurium non-DT104 strains were examined for their ability to grow in tryptic soy broth (TSB) acidified with acetic, lactic, citric, or malic acids at pH 5·4, 4·4, and 3·7. Significantly (P<0·05) higher numbers of S. typhimurium DT104 cells were detected at pH 4·4 and 4·0 in TSB acidified with acetic acid and at pH 4·4 and 3·7 in TSB acidified with lactic acid compared to non-DT104 cells. Acid-shocked and non-shocked (control) cells were plated on TSA (pH 7·3) acidified with lactic acid at pH 5·4, 4·4, and 4·0 and on TSA (pH 7·0±0·2) containing 0·5, 2·5, and 5% sodium chloride. Populations of acid-shockedS. typhimurium DT104 and non DT104 cells recovered on acidified or salt-supplemented TSA were significantly (P<0·05) lower than those of non-shocked cells. A significantly lower number of acid-shocked non-DT104 cells recovered on TSA at pH 5·4, compared to acid-shocked DT104 cells, suggests that DT104 cells may be more resistant to acid shock and subsequent exposure to acid pH. D values and z values of acid-shocked or non-shocked cells of DT104 and non-DT104 strains in liquid whole egg (WE), egg yolk (EY), egg white (EW), whole egg+10% salt (WES), and egg yolk+10% salt (EYS) were determined. Differences in thermal sensitivity of the two types of cells were few. Rates of thermal inactivation of S. typhimurium DT104 cells indicate that the USDA pasteurization process would eliminate >8 log₁₀cfu ml⁻¹of EW heated at 57°C and >11 log₁₀cfu ml⁻¹of WE, EY, WES, or EYS heated at 61°C. D values of acid-shocked DT104 and non-DT104 cells heated in liquid egg products were significantly (P<0·05) lower than those of respective non-shocked cells.