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PubMed2000

Effects of aerobic fitness on fat oxidation and body fatness.

OBJECTIVE: This study investigated the contributions of physical fitness and body composition to 24-h fat oxidation in adults under sedentary conditions in a whole-room calorimeter. METHODS: The following measurements were studied in 109 adults (49 male/45 female) at least 36 h after a bout of exercise: 1) aerobic fitness level assessed by VO2max, 2) body composition determined by underwater weighing, 3) resting metabolic rate (RMR) after an overnight fast, and 4) 24-h energy expenditure (EE) and substrate oxidation determined in a whole-room calorimeter. While in the calorimeter, subjects were provided with a diet (15% protein, 30% fat, and 55% carbohydrate) estimated to produce energy balance on a sedentary day and of similar nutritional composition to their daily dietary intake. RESULTS: We found strong negative correlations between VO2max and % body fat in both male and female subjects, but no relationship between VO2max and 24-h EE under the sedentary conditions of this study. In male subjects, VO2max (mL O2 x kg(-1) fat-free mass x min(-1)) was negatively related to fat oxidation (r = -0.397, P < 0.005), and fat oxidation was more closely related to fat mass (r = 0.434, P < 0.0002) than to fat-free mass (r = 0.165, NS). In contrast, none of these relationships were significant in females. CONCLUSION: The results show that in male subjects under sedentary conditions, 24-h fat oxidation is positively related to body fat mass and negatively related to VO2max (the marker used here for level of physical fitness). This supports our hypothesis that regularly active males maintain lower body fat stores as the low contribution to daily fat oxidation from a lower body fat mass is counterbalanced by the high contribution to fat oxidation from daily physical activity. The lack of a relationship between VO2max and 24-h EE under the sedentary conditions of this study suggests that the major effects of physical activity on total daily EE and fat oxidation may occur during and relatively quickly after an exercise bout. Further, these data also suggest that cessation of regular exercise will likely be associated with a high risk of positive fat balance and weight gain.

Adipose Tissue↗
PubMed2002

Effects of dietary fat types on body fatness, leptin, and ARC leptin receptor, NPY, and AgRP mRNA expression.

Some, but not all, fats are obesogenic. The aim of the present studies was to investigate the effects of changing type and amount of dietary fats on energy balance, fat deposition, leptin, and leptin-related neural peptides: leptin receptor, neuropeptide Y (NPY), agouti-related peptide (AgRP), and proopiomelanocortin (POMC), in C57Bl/6J mice. One week of feeding with a highly saturated fat diet resulted in ~50 and 20% reduction in hypothalamic arcuate NPY and AgRP mRNA levels, respectively, compared with a low-fat or an n-3 or n-6 polyunsaturated high-fat (PUFA) diet without change in energy intake, fat mass, plasma leptin levels, and leptin receptor or POMC mRNA. Similar neuropeptide results were seen at 7 wk, but by then epididymal fat mass and plasma leptin levels were significantly elevated in the saturated fat group compared with low-fat controls. In contrast, fat and leptin levels were reduced in the n-3 PUFA group compared with all other groups. At 7 wk, changing the saturated fat group to n-3 PUFA for 4 wk completely reversed the hyperleptinemia and increased adiposity and neuropeptide changes induced by saturated fat. Changing to a low-fat diet was much less effective. In summary, a highly saturated fat diet induces obesity without hyperphagia. A regulatory reduction in NPY and AgRP mRNA levels is unable to effectively counteract this obesogenic drive. Equally high fat diets emphasizing PUFAs may even protect against obesity.

Adipose Tissue↗
PubMed1998

Dietary fat level and short-term effects of a high-fat meal on food intake and metabolism.

After determining the dietary fat intake in 40 subjects based on a 7-day recording period, the effects of a high-fat breakfast (52% of metabolizable energy from fat) on postprandial fat and carbohydrate metabolism as well as on subsequent lunch intake were investigated in 28 lean, male subjects with habitual dietary fat intakes between 21 and 44% (of daily energy intake). Correlational analysis and comparisons between a low-fat group (LF; fat intake < or =35%, n = 10) and a high-fat group (HF; fat intake > or =40%, n = 11) with a similar body mass index (LF: 22.7, HF: 22.4) and a low body fat content (LF and HF: 10.7) demonstrated that the fat level of the habitual diet did not affect the baseline values and the postprandial changes in the respiratory quotient and in the plasma levels of glucose, insulin, lactate, free fatty acids, beta-hydroxybutyrate, and triglycerides induced by the high-fat breakfast. Only the area under the curve for insulin was higher, and the lactate/insulin ratio was lower in the HF group than in the LF group. Moreover, hunger and satiety ratings and lunch intake (amount, duration, microstructure of eating) after the high-fat breakfast were similar in all subjects. Thus, the habitual level of dietary fat did not alter the acute effects of a fat-rich breakfast on whole-body and hepatic fatty acid oxidation and eating behavior at lunch under the present test conditions. Yet, a long-term high fat intake appears to have subtle effects on postprandial metabolism which are consistent with early signs of a developing insulin resistance.

Adult↗
PubMed1984

Similarity between trans fat and saturated fat in the modification of rat mammary carcinogenesis.

Commercial hydrogenation of vegetable oils results in the introduction of trans fatty acids. In the present study, we have investigated the effect of feeding a fat which contained approximately 38% trans isomers (designated trans fat) on the induction of mammary tumors by dimethylbenz(a)anthracene in rats. The corresponding control fat (designated cis fat), which had a similar fatty acid composition, consisted of only cis isomers. Since both the trans and cis fats were rather saturated, a comparison was also made between these 2 types of fat and corn oil, which contains about 60% linoleic acid (C18:2). Each fat was present in the diet at 2 levels, 5 and 20% by weight. Although rats fed the 20% trans fat or cis fat diets had a slightly higher tumor incidence and yield than did those on the corresponding 5% fat control diets, the difference was not statistically significant. In contrast, rats fed the 20% corn oil diet developed a much greater number of tumors than did rats fed a diet containing only 5% corn oil. Further analysis of the data showed that diets containing either trans fat or cis fat were much less effective than were the corn oil diets in promoting the development of mammary neoplasia at either the 5 or 20% level. Our results thus suggest that trans fat behaves very much like a saturated fat in the modification of mammary tumorigenesis. A determination of the fatty acid content of the mammary fat pad indicated that its composition generally reflected the dietary fatty acid intake, with the incorporation of trans isomers into the mammary tissue found to be dependent on the quantity of trans fat in the diet.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1998

Relative contributions of subcutaneous and intermuscular fat to yields and predictability of retail product, fat trim, and bone in beef carcasses.

Carcass data from one side of 610 steers born from 1988 to 1990 in Cycle IV of the Germ Plasm Evaluation research program were analyzed to develop means for carcass traits and retail product percentages at two fat trim levels (.76 and .00 cm) by yield grade categories. Weights of subcutaneous (s.c.) fat and intermuscular (i.e.m.) fat were recorded separately at each trim level. Quadratic regression curves were plotted for percentages of roast and steak meat (R&S), retail product (RP), and fat trim components relative to incremental changes in USDA yield grade. Prediction equations were developed on a randomly chosen half of the 610 carcasses to predict weights and percentages of R&S, RP, and fat trim using carcass traits obtained at the time of USDA grading and then tested on the remaining half of the carcasses. In addition, prediction equations were developed using s.c. and i.e.m. fat plus carcass traits to evaluate the contribution of each to carcass fabrication yields. Percentage of RP, trimmed to either .76 cm or .00 cm of fat, decreased by an average of 3.5% for each full yield grade increase. Trimming to .00 cm of fat resulted in about 5.3% less RP compared to trimming to .76 cm. A prediction equation for percentage of RP trimmed to .00 cm using adjusted fat thickness, carcass weight, longissimus muscle area, and percentage of kidney knob had an R2 value of .54. The variations in percentage of R&S and percentage of RP at both trim levels were reduced by removing s.c. fat trimmed to .76 cm; however, considerable variation still existed. Subcutaneous fat expressed as a percentage of the sum of i.e.m. and s.c. fat increased as yield grade increased, but the percentage of i.e.m. fat was higher than the percentage of s.c. fat for all yield grades. On the basis of partial correlation coefficients, i.e.m. fat was approximately twice as important as s.c. fat in accounting for variations in fabrication yields.

Adipose Tissue↗
PubMed1987

Use of a fat probe to assess variation in abdominal fat in broilers.

Four trials were conducted to compare the fat probe measure of abdominal fat with that of actual abdominal fat weights and percentage abdominal fat. Various ages, diets, and genetic groups were used to provide experimental chickens with a wide range in body weights and abdominal fat percentages. Mean values obtained by two operators using the probe on the same bird were similar (correlations of .70 to .79). Considering all comparisons, the arithmetic mean of the correlations between fat probe values and percentage abdominal fat was .24; values ranged from .01 to .44. In five comparisons of groups differing significantly in percentage abdominal fat, there were no significant differences in probe values, and correlations between fat and probe values were low. In three other comparisons of groups differing significantly in percentage abdominal fat, differences between probe values were significant and correlations between fat and probe values were moderate. In the comparison groups in which there was an association between probe and fat values, the magnitude of the differences in fat values was about four times as great as that of differences in probe values and the correlations were moderate (.28 to .44). In the comparisons in which higher abdominal fat. In comparisons where higher probe values were not associated with higher abdominal fat, higher body weights were not associated with higher percentage fat.

Adipose Tissue↗
PubMedDate not supplied

Desire to eat high- and low-fat foods following a low-fat dietary intervention.

OBJECTIVE: This study examined changes in desires to eat high-fat and low-fat foods across an obesity treatment program. The hypotheses under examination were (1) preferences for low-fat foods would increase across time and (2) preferences for high-fat foods would decrease across time. DESIGN: Single-group, prospective examination of desires to eat 48 foods, categorized according to fat content, before and after the 16-week treatment program. SETTING: University clinic, Memphis, Tennessee. PARTICIPANTS: 118 obese (mean weight = 194.4 lbs) women (mean age = 45.24 years) participating in an obesity treatment program. INTERVENTION: A 16-week cognitive-behavioral program for obesity. VARIABLES MEASURED: Desires to eat 48 foods varying in fat content and whether or not participants actually ate these foods. ANALYSIS: Analysis of variance, multiple regression, and paired t tests. RESULTS: The results indicate that during the program, preferences for low-fat foods increased, whereas preferences for high-fat foods decreased. These changes mirrored the changes in consumption of both low-fat and high-fat foods. CONCLUSIONS AND IMPLICATIONS: Within a behavioral economic perspective, the reinforcement value of low-fat foods may increase following a low-fat dietary intervention, whereas the reinforcing properties of high-fat foods may decline. This is desirable as low-fat foods hold many advantages over high-fat foods in terms of weight maintenance.

Adult↗
PubMed1998

Effect of fat-free potato chips with and without nutrition labels on fat and energy intakes.

This study investigated the effect on fat and energy intakes of fat-free potato chips made with olestra compared with regular potato chips. Ninety-five participants (unrestrained and restrained males and females) were tested in 2 conditions. In the information condition, participants were given nutrition information about the chips and were aware that the chips differed in fat and energy contents. In the no-information condition, participants were not aware of the differences. In both conditions, participants ate either regular or fat-free potato chips ad libitum for an afternoon snack in a crossover design in two 10-d periods. To assess 24-h intake, participants completed food diaries twice in each 10-d period. The results showed that all groups significantly reduced their fat and energy intakes in the snack when eating the fat-free chips compared with the regular chips (P< 0.0001). Also, potato chip intake did not differ across time for either type of chip. Over 24 h all participants had lower fat intakes (P< 0.05) when eating the fat-free potato chips compared with the regular chips, but 24-h energy intake was not significantly different between groups. When information was provided, restrained participants ate more of the fat-free chips than the regular chips; however, this increase did not negate the reductions in fat and energy associated with eating the fat-free chips. This study showed that substituting fat-free (olestra-containing) potato chips for regular-fat chips can help reduce fat and energy intakes in short-term (within meal) situations and reduce fat intake over 24 h.

Adolescent↗
PubMed1985

Dietary fat intake and taste responses to fat in milk by under-, normal, and overweight women.

Dietary fat intake, with special emphasis on dairy products, was estimated from questionnaires for 42 underweight, 80 normal weight, and 64 overweight adult women. Frequency of consumption of fresh and processed meats, frozen dairy desserts, pastries, and snacks such as potato chips was greater for the overweight than for the underweight subjects. However, preferences between verbally-described high- and low-fat versions of 14 food pairs did not differ by body size. Overweight subjects reported that they consumed more non-fat milk and less whole milk than did the other groups. Discrimination, perceived intensity, paired preference, and hedonic rating of fat in milk and in chocolate milk did not differ significantly according to body size, fat intake, or type of milk consumed. Ad libitum mixing of non-fat milk and "half and half" (12% fat) to individual levels of liking also showed no significant variation with body size. However, subjects with higher dietary fat intakes mixed to higher fat-preference levels in milk than did the low- and medium-fat intake subjects. Those reporting consumption of regular milk (3.5% fat) mixed to higher fat levels than did those who consumed low-fat (2% fat) or non-fat milk. The ad libitum procedure gave better reproducibility and appeared to be a more realistic measure of liking than the hedonic rating or paired-preference tests.

Adolescent↗
PubMed1998

Differences in energy expenditure and substrate oxidation between habitual high fat and low fat consumers (phenotypes).

OBJECTIVE: To investigate physiological differences between habitual high-fat (HF) and low-fat (LF) consumers, which could influence the balance between energy expenditure and energy intake, and the potential for weight gain. SUBJECTS: 16 young, lean males (eight HF and eight LF consumers; % energy from fat 44.3 and 32.0, respectively). MEASUREMENTS: Habitual dietary variables (from FFQ), body mass index (BMI), body fat % (measured by impedance), resting metabolic rate (RMR) (indirect calorimetry), substrate oxidation and basal heart rate, postprandial thermogenesis and heart rate in response to a high-fat (low carbohydrate (CHO)) and high-CHO (low fat) challenge. RESULTS: HF and LF (selected for their intake of fat) did not differ significantly in BMI or % body fat. HF had a significantly higher RMR (1624 vs 1455 kcal/d) and basal heart rate (66 vs 57 bpm) than LF. Differences in oxygen utilisation and heart rate were maintained over a 180 min period, following the high-fat and high-CHO challenge meals. HF had a significantly lower resting respiratory quotient (RQ) than LF and the differences in average RQ were significant over the 180 min examination period. HF had a significantly lower RQ response to the high fat (low CHO) than to the high CHO (low fat) challenge; this effect was not observed in LF. HF had higher total energy intake than LF and a higher absolute (but not %) intake of protein. CONCLUSION: Significant differences in basal energy expenditure and fat oxidation between habitual HF and LF consumers have been observed. The contributions of energy intake and protein intake (g not %) remain to be determined. In this particular group of subjects (young adult males) a high energy intake characterised by a large fat component is associated with metabolic adaptations which could offset the weight inducing properties of a high-fat diet. These physiological differences may be important when considering the relationship between dietary-fat and obesity.

Adolescent↗
PubMed2004

Effects of introducing physical training in the course of a 16-week high-fat diet regimen on hepatic steatosis, adipose tissue fat accumulation, and plasma lipid profile.

OBJECTIVE: We recently reported that an 8-week high-fat diet-induced hepatic steatosis was completely prevented if an exercise training programme was introduced and pursued concurrently with the diet. The purpose of the present study was to determine the extent to which introducing exercise training at mid-point in the course of a 16-week high-fat diet regimen contributes to the reversal of liver lipid infiltration and the reduction of blood lipid profile deterioration and body fat accumulation. DESIGN AND SUBJECTS: Two groups of rats were fed a high-fat diet (42% kcal) for 16 weeks, one remaining sedentary during this entire period (HF-Sed) and the other being exercise trained for the last 8 weeks (HF-Tr). A third group was fed a standard diet and remained sedentary for all 16 weeks (SD-Sed). Training (5 days/week for 8 weeks) began 8 weeks after introducing the high-fat diet and consisted of treadmill running that was progressively increased to reach 60 min at 26 m/min, 10% grade, for the last 4 weeks. MEASUREMENTS: Various parameters including liver lipid infiltration, fat depots and blood lipids. RESULTS: Unexpectedly, liver lipid infiltration was not significantly higher in HF-Sed than in SD-Sed rats (means+/-s.e.: 14.9+/-1.7 vs 12.3+/-0.4 mg/g; P>0.05). High-fat compared to age-matched standard fed rats also showed an absence of difference (P>0.05) in the weight of total visceral fat pads (13%), plasma nonesterified fatty acids (NEFA), and leptin concentrations, but depicted significantly (P<0.01) higher values for subcutaneous fat pad weight and plasma triacyglycerol. Exercise training largely decreased visceral and subcutaneous fat accumulation by 30 and 26%, respectively (P<0.01) as well as NEFA, triacylglycerol, and leptin concentrations (P<0.01). CONCLUSION: Liver lipid infiltration does not seem to progress linearly over 16 weeks of high-fat feeding in light of what has previously been observed after 8 weeks of high-fat feeding. Introducing a training programme in the course of a 16-week high-fat diet protocol reduced adiposity, plasma NEFA, and leptin concentrations below the levels observed in standard fed rats. These data indicate that, exercise training, whether conducted concurrently or introduced during the course of a high-fat diet, is an asset to reduce the deleterious effects of a high-fat diet.

Adipose Tissue↗
PubMed2001

Effects of a high-fat diet on postabsorptive and postprandial testosterone responses to a fat-rich meal.

Postprandial testosterone concentrations have been shown to significantly decrease after a fat-rich meal, which may be due to inhibition of testosterone production by chylomicrons. We examined the effects of a high-fat diet known to reduce postprandial chylomicrons on the testosterone response to a fat-rich meal. Total testosterone (TT), free testosterone (FT), cortisol, and insulin responses to a high-fat test meal containing 5.44 MJ (1,300 kcal, 11% carbohydrate, 3% protein, 86% fat) were determined before (week 0) and after (week 8) an 8-week high-fat diet (64% fat) in 11 healthy men. The high-fat diet resulted in significant reductions in postabsorptive and postprandial serum triacylglycerols (55% and 50%, respectively). There were no significant changes in postabsorptive serum TT, FT, and cortisol, but insulin concentrations were significantly (P < or = .05) lower at week 8 (-28%). There was a significant reduction 1 hour after the fat-rich meal for TT (-22%) and FT (-23%), which remained significantly below baseline for 8 hours. Postprandial TT and FT responses were not significantly different after the 8-week high-fat diet. Postprandial serum cortisol concentrations were significantly reduced 1 hour after the meal. There were no significant differences before and after the high-fat diet. Insulin was significantly increased at the 0-, 1-, and 2-hour postprandial time points before and after the high-fat diet. Compared with week 0, insulin concentrations were significantly lower prior to and immediately after the fat-rich meal at week 8. These data indicate a fat-rich meal results in a prolonged reduction in TT and FT concentrations that is not altered by lowering postprandial chylomicrons. Alternative mechanisms (eg, higher uptake at the receptor level of cells) other than chylomicron-induced or insulin-induced inhibition of steroidogenesis are likely responsible for the reduction in TT and FT after a fat-rich meal.

Administration, Oral↗
PubMed2001

What do users of reduced-fat dairy products know about the fat in their diets?

OBJECTIVES: To assess the fat intake and knowledge about the fat content of foods consumed by a sample of self reported users of reduced-fat dairy products. DESIGN: Cross-sectional study of a population-based sample of women shoppers. SETTING: A small, rural town (population approximately 6000) in central Victoria, Australia. SUBJECTS: Seventy-eight women aged 25-50 years, who regularly used at least one reduced-fat dairy product. RESULTS: Mean reported intake of total fat was lower while intake of dairy fat was similar to that of a national sample of women of the same age both in the whole sample and when under-reporters were excluded. The ability to identify major sources of fat in the diet as reported appeared to be limited. Less than half of the subjects were able to correctly estimate the fat content of reduced-fat dairy products relative to regular products and about one quarter of subjects reported replacing one kind of oil or fat with another as a strategy to reduce fat intake. Subjects were generally aware of the need to 'eat less fat' but few could articulate specific recommendations. A number of subjects reported using low fat diets to control their weight but few subjects appeared to understand the connection between fat intake and energy intake. CONCLUSIONS: The findings of this study raise important questions about how nutrition advice is understood and implemented by consumers, particularly the message to reduce fat intake and the role of energy balance in weight management. They also highlight the difficulty of interpreting information on food intake, in subjects who have modified their diet by reducing intake of specific foods.

Adult↗
PubMed1997

Effect of high-fat and low-fat diets on voluntary energy intake and substrate oxidation: studies in identical twins consuming diets matched for energy density, fiber, and palatability.

There remains controversy over the effects of dietary fat content on voluntary energy intake. Additionally, the question of whether there is a genetic susceptibility to overeating high-fat diets has not been resolved. To address these issues, we designed two diets: a low-fat diet providing approximately 20% of energy as fat and a high-fat diet with approximately 40% of energy as fat. The diets were matched for energy density, fiber, and palatability. In a two-phase, 18-d intervention study, voluntary energy intakes and macronutrient oxidation rates during the fasting and fed states were determined in seven pairs of identical male twins. In contrast with results of previous intervention studies, in which low-fat and high-fat diets were not matched for energy density and other associated variables, we observed no significant difference in voluntary energy intake between the low-fat and high-fat phases, and mean daily intakes were similar (10.3 and 10.7 MJ/d, respectively). Postprandial rates of fat oxidation tended to reflect fat intakes in the two dietary phases, thus helping to explain the lack of a difference in mean energy intakes. There was also a significant twin-pair similarity in differences in energy intakes between dietary phases (P = 0.013). These results suggest that dietary fat content does not have a major influence on voluntary energy intake when dietary variables usually associated with fat are controlled for and that there may be a familial influence on the effects of dietary fat content on energy intake.

Adult↗
PubMed1991

Physiological response of mature rats to replacement of dietary fat with a fat substitute.

The effects of replacing dietary fat with a fat substitute on food intake, body composition and lipid metabolism were examined in rats. Female Sprague-Dawley rats (250 g) were fed diets containing between 2 and 63% of energy as fat for 64 d. Inclusion of a substitute resulted in diets of different fat content but similar texture. When 10% corn oil (21% kJ-fat diet) was replaced with the substitute supplemented with linoleic acid (2% kJ-fat diet), rats increased food intake so that there was no effect on energy intake, body weight, body composition or serum lipid profile. Rats fed a diet containing 10% corn oil and 30% Crisco vegetable shortening (63% kJ-fat diet) became obese and hyperinsulinemic. When half (51% kJ-fat diet) or all (30% kJ-fat diet) of the Crisco was replaced with the fat substitute, the rats increased food intake and were fatter than controls but less obese than rats fed the 63% kJ-fat diet. Hepatic lipid oxidation and ketone synthesis were proportional to the percentage of dietary energy as fat. Adipocyte de novo lipid synthesis was inhibited by 51% kJ-fat and 63% kJ-fat diets. Partial or total replacement of Crisco prevented the hyperinsulinemia observed in 63% kJ-fat rats, suggesting a protective effect against the development of insulin resistance with diet-induced obesity.

Animals↗
PubMed2001

Low-fat diet alters intramuscular substrates and reduces lipolysis and fat oxidation during exercise.

We determined whether a low-fat diet reduces intramuscular triglyceride (IMTG) concentration, whole body lipolyis, total fat oxidation, and calculated nonplasma fatty acid (FA) oxidation during exercise. Seven endurance-trained cyclists were studied over a 3-wk period during which time they exercised 2 h/day at 70% of maximum O2 uptake VO(2 max) and consumed approximately 4,400 kcal/day. During the 1st wk, their fat intake provided 32% of energy. During the 2nd and 3rd wk, they were randomly assigned to eat 2 or 22% of energy from fat (2%FAT or 22%FAT). Compared with 22%FAT, 2%FAT lowered IMTG concentration and raised muscle glycogen concentration at rest (P < 0.05). Metabolism was studied during 1 h of exercise at 67% VO(2 max) performed in the fasted state. 2%FAT resulted in a 27% reduction (P < 0.05) in total fat oxidation vs. 22%FAT without altering the stable isotopically determined rates of plasma free fatty acid or glucose disappearance. Therefore, 2%FAT reduced calculated nonplasma FA oxidation by 40% in association with a 19% reduction in whole body lipolysis while increasing calculated minimal muscle glycogen oxidation compared with 22%FAT (all P < 0.05). In summary, an extremely low fat (2% of energy) and high-carbohydrate diet lowers whole body lipolysis, total fat oxidation, and nonplasma FA oxidation during exercise in the fasted state in association with a reduced concentration of intramuscular triglyceride.

Adult↗
PubMed2006

Milk fat thermal properties and solid fat content in emmental cheese: a differential scanning calorimetry study.

The experiments reported in this study give deeper insight into the crystallization of milk fat in Emmental cheese, which is the most widely consumed hard cheese in France. Differential scanning calorimetry (DSC) was used to monitor the thermal properties of milk fat after the main stages involved during manufacture of Emmental cheese. By heating the samples to 60 degrees C to eliminate their thermal history and cooling them at 2 degrees C/min, the liquid --> solid phase transition of fat was investigated. Confocal laser scanning microscopy was used to characterize in situ the supramolecular organization of milk fat dispersed in the casein matrix. The destabilization of fat globules by aggregation or coalescence and the formation of free fat during the manufacture altered the thermal properties of milk fat by increasing the initial temperature of crystallization and by the formation of 2 overlapping exotherms. The melting properties of the crystalline structures formed by fat at the temperatures used for ripening (12, 21, and 4 degrees C) were examined. Differential scanning calorimetry was used to determine the ratio of solid to liquid fat; that is, the amount of fat that is crystallized, by dividing the partial enthalpy of melting of the fat for ripening temperature by the total enthalpy of melting of the same fat extracted from cheese. This study shows, for the first time, that milk fat is partially crystallized in Emmental cheese: about 55.7 +/- 3.5% of fat is solid at 4 degrees C at the end of ripening. Polymorphic phase transitions of milk fat are also suggested during ripening of Emmental cheese.

Animals↗
PubMed2004

Factors that contribute to the botulinal safety of reduced-fat and fat-free process chesse products.

The effects of fat, type of natural cheese, and adjunct process cheese ingredients were evaluated to determine factors that contribute to the botulinal safety of reduced-fat (RF) process cheese products stored at 30 degrees C. In the first set of experiments, pasteurized process cheese products (PPCPs) were formulated using full-fat (FF) Cheddar, 30% RF Cheddar, or skim milk (SM) cheese as cheese-base types and were standardized to 59% moisture, pH 5.75, 2.8 or 3.2% total salts, and 15 to 19% fat. Subsequent trials evaluated the effect of fat levels and adjunct ingredients in PPCPs made with SM, RF, and FF cheese (final fat levels, less than 1, 13, and 24%, respectively). When fat levels of PPCPs were comparable (15.1, 19.1, and 16.2 for product manufactured with SC, RE and FF cheese, respectively), botulinal toxin production was delayed for up to 2 days in PPCPs formulated with SM compared with RF or FF cheese; however, the effect was not statistically significant. When fat levels were reduced to less than 1% in SM PPCPs, toxin production was delayed 2 weeks in products made with SM compared with RF or FF cheese manufactured with 13 or 24% fat, respectively. The antibotulinal effect of adjunct ingredients varied among the products manufactured with different fat levels. Sodium lactate significantly delayed toxin production (P < 0.05) for all fat levels tested, whereas beta-glucan fat replacer did not delay toxin production. An enzyme-modified cheese used as a flavor enhancer significantly delayed toxin production (P < 0.05) in SM (less than 1% fat) products but had little to no inhibitory effect in RF (13% fat) and FF (24% fat) cheese products. Similarly, monolaurin increased the time to detectable toxin in SM products but was ineffective in RF or FF cheese products. These results verify that RF PPCPs exhibit greater safety than FF products and that safety may be enhanced by using certain adjunct ingredients as antimicrobials.

Botulinum Toxins↗