Analysis of free fatty acids in whey products by solid-phase microextraction

Advanced micro-extraction techniques (SPME, HiSorb) for the determination of goat cheese whey wastewater VOCs

HiSorb and solid-phase microextraction (SPME), two environmentally friendly micro-extraction techniques based on the same fundamental principles, were evaluated for their extraction efficiency of volatile organic compounds (VOCs) from goat cheese whey wastewater. For this purpose, a sample preparation method based on the headspace-HiSorb technique was developed and evaluated for its efficiency in terms of the amount of extracted compounds and reproducibility of results. Thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) and GC/MS analytical methods were used to perform the wastewater analysis, respectively. The experimental parameters of HiSorb were evaluated in terms of probe coating, extraction time, stirring speed, sample volume, extraction temperature and salt addition. Under optimal extraction conditions, it was observed that the use of the divinylbenzene/carbon wide range/polydimethylsiloxane (DVB/CWR/PDMS) triple coating for HiSorb and DVB/Carboxen (CAR)/PDMS for SPME, was best suited to extract a broader range of VOCs with higher peak intensities. A total of 34 VOCs were extracted and determined with the DVB/CWR/PDMS HiSorb probe, while only 23 VOCs were determined with the conventional DVB/CAR/PDMS SPME fiber. The DVB/CWR/PDMS HiSorb probe has a higher adsorbent capacity which results in a higher sensitivity for VOCs compared to the DVB/CAR/PDMS SPME fiber. Furthermore, the HiSorb technique exhibits better reproducibility, as indicated by the lower relative standard deviation (RSD) of 3.7% compared to 7.1% for SPME. Therefore, the HiSorb technique is an effective method for detecting VOCs in complex matrices, such as wastewater.

Antioxidant Potential of the Sweet Whey-Based Beverage Colada after the Digestive Process and Relationships with the Lipid and Protein Fractions

Whey-based beverages could be an effective way of reusing a by-product of th cheese industry, mitigating environmental hazards and, at the same time, profiting a useful food with high nutritional and antioxidant properties. In this study, a traditional Ecuadorian beverage (Colada) was prepared combining sweet whey, Maracuyá and barley. Antioxidant properties before and after an in vitro digestion using the INFOGEST method were determined, and relationships with intestinal transformations of the lipid and protein fractions were analyzed. The digestive process had a positive effect on antioxidant properties based on increased values of ABTS and FRAP located in the bioaccessible fraction (BF), together with strong increments of total polyphenols. Moreover, pretreatment of Caco-2 cells with the BF of Colada significantly reduced ROS generation (p < 0.001) measured by the dichlorofluorescein assay. Substantial changes of the fatty acid profile occurred during digestion, such as a fall of saturated fatty acids and a rise of polyunsaturated. The protein profile, examined by SDS-PAGE and exclusion molecular chromatography in the BF, showed that the major part of the proteins were digested in the intestinal phase. Analysis of NanoLC-MS/MS revealed 18 antioxidant peptides originated from whey proteins, but also 16 peptides from barley with potential antioxidant properties. In conclusion, combining sweet whey with Maracuyá and barley constitutes an excellent nutritional beverage with a strong antioxidant potential.

Fast quantification of short-chain fatty acids in rat plasma by gas chromatography

Short-chain fatty acids (SCFAs) are the main metabolites of the intestinal flora and play an important role in the interaction between the intestinal flora and host metabolism. Therefore, reliable methods are needed to accurately measure SCFAs concentrations. SCFAs are commonly analyzed by gas chromatography-mass spectrometry (GC-MS), which requires lengthy sample treatments and a long run time. This study aimed to develop a fast GC method with formic acid pretreatment for SCFAs quantification in the plasma of rat. Baseline chromatographic resolution was achieved for three SCFAs (acetic, propionic, and butyric) within an analysis time of 10.5 min. The method exhibited good recovery for a wide range of concentrations with a low limit of detection for each compound. The relative standard deviations (RSDs) of all targeted compounds showed good intra- and interday precision (<10%). We used our method to measure SCFAs levels in plasma samples from rats fed with a high fructose diet (HFD) to test the accuracy of the developed method. It was shown that SCFAs are indeed affected negatively by a HFD (60% fructose). This method was successfully employed to accurately determine SCFAs in the rat plasma with minimum sample preparation. Results showed potential damage of HFD, which produced lower SCFAs. PRACTICAL APPLICATION: Increasingly, microbiota and gut health research are being conducted by many food scientists to elucidate the relationships among the factors of food components, particularly the nondigestible carbohydrates, food processing conditions, and potential health impact. This research provides a useful, rapid, and accurate method that can save time in the analysis of short-chain fatty acids, which are commonly analyzed in gut health research.

Endogenous level of acetic acid in yellowfin tuna (Thunnus albacares): a pilot study about a possible controversy on its residue nature

A method based on headspace solid-phase microextraction (HS-SPME) followed by GC-MS analysis was developed for the determination of underivatised acetic acid in fresh tuna fish muscle. Parameters such as the fibre selected and the extraction time and temperature were optimised and the linearity, detection limits and precision of the whole analytical procedure were assessed. The method was then applied to determine the acetic acid concentration in fresh yellowfin tuna muscles (Thunnus albacares) in order to evaluate the endogenous level and its variations during the shelf life under different storage conditions. A qualitative comparison was also made with variations in histamine levels to evaluate the possibility of the joint monitoring of acetic acid and histamine to identify fish stored in poor conditions. The caudal area always had a lower content of acetic acid than the ventral area, independent of the storage time and temperature. A difference was found between the 6- and 3-day time points and day 0 at a storage temperature of 8°C and between the 6-day time point and day 0 at a storage temperature of 0°C, independent of the anatomical area of the sampled tissue. The evaluation of acetic acid could represent an important approach in the field of food safety to detect the illicit use of acetic acid as an antibacterial preservative treatment or to eliminate the unpleasant smell of trimethylamine.

Detection of Nonesterified (Free) Fatty Acids in Bovine Serum: Comparative Evaluation of Two Methods

A method comparison study for the determination and quantitation of nonesterified fatty acids (NEFAs) in serum, using the commercial “NEFA C” enzymatic test kit, was performed using the spectrophotometric method recommended by the manufacturer and a modified procedure optimized for the use of a microplate reader, a 96-well microtiter plate, and small sample volumes (10 μl). Linearity, sensitivity, and precision using the test kit were determined for each method of detection. The assay was linear from 0 to 1.97 mEq/liter for both procedures, and the limits of detection were determined to be 0.22 (±0.074) and 0.05 (±0.002) mEq/liter for the spectrophotometer and microplate reader, respectively. Pairs of measurements for bovine serum samples were compared and evaluated by a mean difference plot method and not regression analysis, a method that has been shown to be inappropriate for method comparison studies. The difference plot was used to evaluate the systematic bias between the 2 methods. Random error is reported on the basis of SD differences, and “limits of agreement” are used to describe the maximum differences likely to occur between the 2 methods. Results suggest that the microplate reader method can be used reliably in place of the recommended spectrophotometric method. The microplate reader method is preferred because of its high throughput capabilities, simultaneous analysis of all the standards and samples, use of small sample and reagent volumes, and reduction in labor requirements and costs.

Phytochemical analysis, antioxidant activity, fatty acids composition, and functional group analysis of Heliotropium bacciferum

Heliotropium bacciferum is paramount in medicinal perspective and belongs to Boraginaceae family. The crude and numerous fractions of leaves, stem, and roots of the plant were investigated for phytochemical analysis and DPPH radical scavenging activity. Phytochemical analysis of crude and fractions of the plant revealed the presence of alkaloids, saponins, tannins, steroids, terpenoids, flavonoids, glycosides, and phenols. The antioxidant (free radical scavenging) activity of various extracts of the Heliotropium bacciferum was resolute against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical with the avail of UV spectrophotometer at 517 nm. The stock solution (1000 mg/mL) and then several dilutions (50, 100, 150, 200, and 250 mg/mL) of the crude and fractions were prepared. Ascorbic acid was used as a standard. The plant leaves (52.59 ± 0.84 to 90.74 ± 1.00), stem (50.19 ± 0.92 to 89.42 ± 1.10), and roots extracts (49.19 ± 0.52 to 90.01 ± 1.02) divulged magnificent antioxidant activities. For the ascertainment of the fatty acid constituents a gas chromatograph hyphenated to mass spectrometer was used. The essential fatty acids for growth maintenance such as linoleic acid (65.70%), eicosadienoic acid (15.12%), oleic acid (8.72%), and palmitic acid (8.14%) were found in high percentage. The infrared spectra of all extracts of the plant were recorded by IR Prestige-21 FTIR model.

Homogenization and lipase treatment of milk and resulting methyl ketone generation in blue cheese

A specific range of methyl ketones contribute to the distinctive flavor of traditional blue cheeses. These ketones are metabolites of lipid metabolism by Penicillium mold added to cheese for this purpose. Two processes, namely, the homogenization of milk fat and the addition of exogenous lipase enzymes, are traditionally applied measures to control the formation of methyl ketones in blue cheese. There exists little scientific validation of the actual effects of these treatments on methyl ketone development. The present study evaluated the effects of milk fat homogenization and lipase treatments on methyl ketone and free fatty acid development using sensory methods and the comparison of selected volatile quantities using gas chromatography. Initial work was conducted using a blue cheese system model; subsequent work was conducted with manufactured blue cheese. In general, there were modest effects of homogenization and lipase treatments on free fatty acid (FFA) and methyl ketone concentrations in blue cheese. Blue cheese treatments involving Penicillium roqueforti lipase with homogenized milk yielded higher FFA and methyl ketone levels, for example, a ∼20-fold increase for hexanoic acid and a 3-fold increase in 2-pentanone.

Influence of heating and acidification on the flavor of whey protein isolate

Previous studies have established that whey protein manufacture unit operations influence the flavor of dried whey proteins. Additionally, manufacturers generally instantize whey protein isolate (WPI; ≥ 90% protein) by agglomeration with lecithin to increase solubility and wettability. Whey protein isolate is often subjected to additional postprocessing steps in beverage manufacturing, including acidification and heat treatment. These postprocessing treatments may further influence formation or release of flavors. The objective of the first study was to characterize the effect of 2 processing steps inherent to manufacturing of acidic protein beverages (acidification and heat treatment) on the flavor of non-instant WPI. The second study sought to determine the effect of lecithin agglomeration, a common form of instantized (INST) WPI used in beverage manufacturing, on the flavor of WPI after acidification and heat treatment. In the first experiment, commercial non-instantized (NI) WPI were rehydrated and evaluated as is (control); acidified to pH 3.2; heated to 85°C for 5 min in a benchtop high temperature, short time (HTST) pasteurizer; or acidified to 3.2 and heated to 85°C for 30s (AH-HTST). In the second experiment, INST and NI commercial WPI were subsequently evaluated as control, acidified, heated, or AH-HTST. All samples were evaluated by descriptive sensory analysis, solid-phase microextraction (SPME), and gas chromatography-mass spectrometry. Acidification of NI WPI produced higher concentrations of dimethyl disulfide (DMDS) and sensory detection of potato/brothy flavors, whereas heating increased cooked/sulfur flavors. Acidification and heating increased cardboard, potato/brothy, and malty flavors and produced higher concentrations of aldehydes, ketones, and sulfur compounds. Differences between INST and NI WPI existed before treatment; INST WPI displayed cucumber flavors not present in NI WPI. After acidification, INST WPI were distinguished by higher intensity of cucumber flavor and higher concentrations of E-2-nonenal. No perceivable differences were observed between INST and NI WPI after heating; sulfur and eggy flavors increased in both types of WPI. After treatment, AH-INST-HTST samples were differentiated from AH-NI-HTST by grassy/hay and grainy flavor and increased lipid oxidation products. Further processing of WPI in food applications has negative effects on the flavor contributions of WPI.

The impact of antioxidant addition on flavor of cheddar and mozzarella whey and cheddar whey protein concentrate

Lipid oxidation products are primary contributors to whey ingredient off-flavors. The objectives of this study were to evaluate the impact of antioxidant addition in prevention of flavor deterioration of fluid whey and spray-dried whey protein. Cheddar and Mozzarella cheeses were manufactured in triplicate. Fresh whey was collected, pasteurized, and defatted by centrifugal separation. Subsequently, 0.05% (w/w) ascorbic acid or 0.5% (w/w) whey protein hydrolysate (WPH) were added to the pasteurized whey. A control with no antioxidant addition was also evaluated. Wheys were stored at 3 degrees C and evaluated after 0, 2, 4, 6, and 8 d. In a subsequent experiment, selected treatments were then incorporated into liquid Cheddar whey and processed into whey protein concentrate (WPC). Whey and WPC flavors were documented by descriptive sensory analysis, and volatile components were evaluated by solid phase micro-extraction with gas chromatography mass spectrometry. Cardboard flavors increased in fluid wheys with storage. Liquid wheys with ascorbic acid or WPH had lower cardboard flavor across storage compared to control whey. Lipid oxidation products, hexanal, heptanal, octanal, and nonanal increased in liquid whey during storage, but liquid whey with added ascorbic acid or WPH had lower concentrations of these products compared to untreated controls. Mozzarella liquid whey had lower flavor intensities than Cheddar whey initially and after refrigerated storage. WPC with added ascorbic acid or WPH had lower cardboard flavor and lower concentrations of pentanal, heptanal, and nonanal compared to control WPC. These results suggest that addition of an antioxidant to liquid whey prior to further processing may be beneficial to flavor of spray-dried whey protein. Practical Application: Lipid oxidation products are primary contributors to whey ingredient off-flavors. Flavor plays a critical and limiting role in widespread use of dried whey ingredients, and enhanced understanding of flavor and flavor formation as well as methods to control or minimize flavor formation during processing are industrially relevant. The results from this study suggest that addition of an antioxidant to liquid whey prior to further processing may be beneficial to minimize flavor of spray-dried whey protein.

Starter bacteria are the prime agents of lipolysis in cheddar cheese

To assess the contribution of starter lactic acid bacteria (LAB) to lipolysis in Cheddar cheese, the evolution of free fatty acids (FFAs) was monitored in Cheddar cheeses manufactured from pasteurized milks with or without starter. Starter-free cheeses were acidified by a combination of lactic acid and glucono-delta-lactone. Starter cultures were found to actively produce FFAs in the cheese vat, and mean levels of FFAs were significantly higher in starter cheeses over ripening. The contribution of nonstarter LAB toward lipolysis appears minimal, especially in starter-acidified cheeses. It is postulated that the moderate increases in FFAs in Cheddar cheese are primarily due to lack of access of esterase of LAB to suitable lipid substrate. The results of this study indicate that starter esterases are the primary contributors to lipolysis in Cheddar cheese made from good quality pasteurized milk.

Rapid determination of short-chain fatty acids in colonic contents and faeces of humans and rats by acidified water-extraction and direct-injection gas chromatography

Short-chain fatty acids (SCFAs) have attracted much attention recently because of their positive physiological effects. In this work, a rapid and reliable gas chromatographic method for determination of eight SCFAs, in colonic and faecal samples from rats and humans has been developed and validated. The methodology involves extraction of the SCFAs in water before a direct injection procedure on a FFAP capillary column. A stock standard solution containing acetic acid, propionic acid, n-butyric acid, i-butyric acid, n-valeric acid, i-valeric acid, n-caproic acid and n-heptanoic acid was prepared and used. A high linearity (r2 > 0.9990), low quantification limit (2.38-30.14 microm) and high recovery for most acids were obtained. Acidification of faecal samples was found to be crucial for quantitative determination of the SCFAs, and adjustment of pH to 2-3 was regarded as necessary. Glass wool inserted in the glass liner of the injection port proved effective in preventing the contamination of the column by non-volatiles, and 12% formic acid reduced the ghost peak that appeared gradually after several injections. After validation, the methodology was applied on two faecal samples from rats fed diets containing different amount of dietary fibre and one faecal sample from human fed a normal diet to test the accuracy of the developed method.

Ion-pair dynamic liquid-phase microextraction combined with injection-port derivatization for the determination of long-chain fatty acids in water samples

Ion-pair dynamic liquid-phase microextraction coupled to injection-port derivatization has been developed for the determination of long-chain fatty acids in water samples by gas chromatography-mass spectrometry (GC-MS). In this procedure, long-chain fatty acids (C(14), C(16) and C(18)) were converted into their ion-pair complexes with tetrabutylammonium hydrogen sulfate and then extracted by organic solvent (1-octanol) impregnated in the hollow fiber. The dynamic nature of the extraction was represented by the repeated movement of the acceptor phase (organic solvent) in the hollow fiber that was controlled by a syringe pump. Ion pairs of fatty acids quantitatively formed butyl esters in the injection-port of the gas chromatography. Several parameters such as injection temperature, purge-off time, organic solvent, ion-pair reagent, pH, agitation speed, extraction time and the syringe pump parameters (plunger speed and dwell time) have been optimized. The limits of detection were in the range 0.0093-0.015 ng mL(-1) (at a signal-to-noise ratio of 3) under GC-MS-selected ion monitoring mode and the relative standard deviations were between 7.7% and 11.5%. The method was successfully applied to measure long-chain fatty acids in real water samples.

Characterization of Dried Whey Protein Concentrate and Isolate Flavor

The flavor of whey protein concentrates (WPC 80) and whey protein isolates (WPI) was studied using instrumental and sensory techniques. Four WPC 80 and 4 WPI, less than 3 mo old, were collected in duplicate from 6 manufacturers in the United States. Samples were rehydrated and evaluated in duplicate by descriptive sensory analysis. Duplicate samples with internal standards were extracted with diethyl ether. Extracts were then distilled to remove nonvolatile material using high vacuum distillation. Volatile extracts were analyzed using gas chromatography/olfactometry with post peak intensity analysis and aroma extract dilution analysis. Compounds were identified by comparison of retention indices, odor properties, and gas chromatography/mass spectrometry against reference standards. Whey proteins exhibited sweet aromatic, cardboard/wet paper, animal/wet dog, soapy, brothy, cucumber, and cooked/milky flavors, along with the basic taste bitter, and the feeling factor astringency. Key volatile flavor compounds in WPC 80 and WPI were butanoic acid (cheesy), 2-acetyl-1-pyrroline (popcorn), 2-methyl-3-furanthiol (brothy/burnt), 2,5-dimethyl-4-hydroxy-3-(2H)-furanone (maple/spicy), 2-nonenal (fatty/old books), (E,Z)-2,6-nonadienal (cucumber), and (E,Z)-2,4-decadienal (fatty/oxidized). This baseline data on flavor and flavor sources in whey proteins will aid ongoing and future research and will help to identify the most appropriate whey ingredients to use to control or minimize flavor variability in whey enhanced products.

The Effect of Lactococcus lactis Starter Cultures on the Oxidative Stability of Liquid Whey

The oxidative stability of liquid Cheddar cheese whey was evaluated using 2 Lactococcus lactis starter cultures in combination and alone along with a control, utilizing glucono-delta-lactone for acid development. Fresh and stored whey were evaluated for volatile composition, free fatty acids, and flavor by descriptive sensory analysis. A significant increase in volatile lipid oxidation products, most notably, hexanal, occurred during storage, and a corresponding decline in the free fatty acid linoleic acid was found. The flavor and aroma characteristic, cardboardy, was correlated to the increase in volatile lipid oxidation products and the decline in linoleic acid. Evidence strongly suggested that lipid oxidation was initiated during whey production and escalated during storage and that the starter cultures significantly influenced the level of volatile lipid oxidation products. Further understanding of the impact of starter cultures on whey may allow for the production of higher quality whey ingredients with wider food application.

Determining flavor and flavor variability in commercially produced liquid cheddar whey

Dried whey and whey protein are important food ingredients. Functionality of whey products has been studied extensively. Flavor inconsistency and flavors which may carry through to the finished product can limit whey ingredient applications in dairy and nondairy foods. The goal of this research was to determine the flavor and flavor variability of commercially produced liquid Cheddar cheese whey. Liquid Cheddar cheese whey from five culture blends from two different stirred-curd Cheddar cheese manufacturing facilities was collected. Whey flavor was characterized using instrumental and sensory methods. Wide variation in whey headspace volatiles was observed between different manufacturing facilities (P < 0.05). Hexanal and diacetyl were two key volatiles that varied widely (P < 0.05). FFA profiles determined by solid-phase microextraction and degree of proteolysis of the whey samples were also different (P < 0.05). Differences in whey flavor profiles were also confirmed by descriptive sensory analysis (P < 0.05). Differences in liquid whey flavor were attributed to differences in milk source, processing and handling and starter culture blend. The flavor of liquid Cheddar cheese whey is variable and impacted by milk source and starter culture rotation. Results from this study will aid future studies that address the impact of liquid whey flavor variability on flavor of dried whey ingredients.