Rapid method for cholesterol analysis in bovine milk and options for applications

Non-enzymatic electrochemical determination of cholesterol in dairy products on boron-doped diamond electrode

Determination of cholesterol in food matrices is essential for quality control concerning the health of consumers. Herein, a simple electrochemical approach for cholesterol quantitation in dairy products is evaluated. The newly developed differential pulse voltammetric method using acetonitrile-perchloric acid mixture as a supporting electrolyte is statistically compared to GC-MS and HPLC-UV. Oxidation signals of cholesterol at +1.5 V and +1.4 V (vs. Ag/AgNO₃ in acetonitrile) provide detection limits of 4.9 µM and 6.1 µM on boron-doped diamond and glassy carbon electrodes, respectively. A simple liquid-liquid extraction procedure from dairy products into hexane resulted in a recovery rate of (74.8 ± 3.8)%. The method provides results in close agreement (at a 95% confidence level) with GC-MS, while HPLC-UV resulted in a significant difference in estimated cholesterol concentrations for all samples. This newly developed method is a simpler, faster and cheaper alternative to instrumentally demanding MS-based methods and clearly outperforms HPLC-UV.

Immobilization of horseradish peroxidase on lysine-functionalized gum Arabic-coated Fe3O4 nanoparticles for cholesterol determination

BACKGROUND

Horseradish Peroxidase (HRP) is ranked as one of the most important industrial enzymes that is extensively used in industry. Cholesterol is routinely detected indirectly by cholesterol oxidase in the presence of O₂, liberating H₂O₂ as a by-product. The H₂O₂ content is determined through the HRP activity in the presence of a redox dye, producing a red colored quinoneimine which can be measured quantitatively. Herein, we have designed a magnetic nanoparticle for reusing and easily separating HRP as the most expensive compartment for the low-cost cholesterol assay.

METHODS

The gum Arabic coated magnetic nanoparticles were functionalized with L-lysine linker for maintaining protein flexibility on nanoparticle. Enzyme-loaded nanoparticles were characterized by TEM, FTIR, DLS, VSM and XRD analysis.

RESULTS

The immobilization efficiency was ∼65% and the immobilized HRP retained 60% of its activity after 8 times reuse. The optimum pH and thermal stability shifted from 7.0 to 8.0 and 60 to 70 °C after immobilization, respectively. Storage stability of HRP was improved by 10%, at 4 °C for 60 days. Immobilized HRP showed more catalytic activity in presence of Fe²⁺, Ca²⁺ and Na⁺. The designed system has cholesterol detection linearity range from 0.2 to 5.0 mM and detection limit of 0.08 mM and acceptable correlation coefficient of 0.9973 and 0.9982 on sample serum using both chromogens.

CONCLUSION

The HRP-loaded magnetic nanoparticles are capable of being used as a cost-effective system for cholesterol determination in laboratory due to its reusability and stability benefits.

Development of colorimetric cholesterol detection kit using TPU nanofibre/cellulose acetate membrane

In this study, the authors report a simple fabrication of thermoplastic polyurethane (TPU) nanofibres-based kit for cholesterol detection. TPU is a polymer that is highly elastic, resistant to microorganisms, abrasion and compatible with blood; thus, making it a natural selection as an immobilisation matrix for cholesterol oxidase (ChOx) enzyme. The nanofibre was fabricated by electrospinning process and was characterised using scanning electron microscopy and Fourier transform-infrared spectroscopy. ChOx was covalently immobilised on TPU nanofibre and cholesterol level/concentration was visually found using 4-aminoantipyrine, a dye that reacts with H₂O₂ produced from the oxidation of cholesterol by ChOx and changes colour from yellow to red. The efficacy of the nanofibre to act as a detecting substrate was compared with cellulose acetate (CA) membrane, a well-documented enzyme immobilisation matrix. The optimisation of enzyme concentration and dye quantity were performed using standard ChOx spectrophotometric assay and the same was used in CA membrane and TPU nanofibre. The ChOx immobilised nanofibre showed good linear range from 2 to 10 mM with a lower detection limit of 2 mM and was highly stable compared to that of CA membrane. The enzyme immobilised nanofibre was further validated in serum samples.

Invited review: Growth-promoting effects of colostrum in calves based on interaction with intestinal cell surface receptors and receptor-like transporters

The postnatal development and maturation of the gastrointestinal (GI) tract of neonatal calves is crucial for their survival. Major morphological and functional changes in the calf's GI tract initiated by colostrum bioactive substances promote the establishment of intestinal digestion and absorption of food. It is generally accepted that colostrum intake provokes the maturation of organs and systems in young calves, illustrating the significance of the cow-to-calf connection at birth. These postnatal adaptive changes of the GI tissues in neonatal calves are especially induced by the action of bioactive substances such as insulin-like growth factors, hormones, or cholesterol carriers abundantly present in colostrum. These substances interact with specific cell-surface receptors or receptor-like transporters expressed in the GI wall of neonatal calves to elicit their biological effects. Therefore, the abundance and activity of cell surface receptors and receptor-like transporters binding colostral bioactive substances are a key aspect determining the effects of the cow-to-calf connection at birth. The present review compiles the information describing the effects of colostrum feeding on selected serum metabolic and endocrine traits in neonatal calves. In this context, the current paper discusses specifically the consequences of colostrum feeding on the GI expression and activity of cell-receptors and receptor-like transporters binding growth hormone, insulin-like growth factors, insulin, or cholesterol acceptors in neonatal calves.

Differences in milk fat composition from four old sheep breeds

Abstract. The present short communication presents a comparison between the milk fat composition of four old sheep breeds. All animals were fed the same diet and a milk sample was obtained at the same lactation day and analyzed for its major components, cholesterol concentration and a complete fatty acid profile. From all studied candidates, the Walachian breed (also when compared with modern breeds employed in the dairy industry) was determined to have the most suitable milk composition for human health.

Alternative to decrease cholesterol in sheep milk cheeses

The presence of cholesterol in foods is of nutritional interest because high levels of this molecule in human plasma are associated with an increasing risk of cardiovascular disease and nowadays consumers are demanding healthier products. The goal of this experiment was to diminish the cholesterol content of Manchego, the most popular Spanish cheese manufactured from ewes milk. For this purpose three bulk milks coming from dairy ewe fed with 0 (Control), 3 and 6% of linseed supplement on their diet were used. Nine cheeses (3 per bulk milk) were manufactured and ripened for 3 months. Cholesterol of ewes milk cheese from 6% to 12% linseed supplemented diets decreased by 9.6% and 16.1% respectively, therefore supplying a healthier profile. In a second experiment, different sources of unsaturated fatty acids (rich in oleic, linoleic and α-linolenic acids) were supplemented to dairy ewes and no significant differences were found on cheese cholesterol levels.

Effect of dietary extruded linseed, verbascoside and vitamin E supplements on yield and quality of milk in Lacaune ewes

Milk yield and milk qualitative parameters were evaluated in Lacaune ewes on a diet supplemented with extruded linseed, verbascoside and vitamin E. A 98 d-trial was conducted on 44 ewes and started 40±2 d post partum. The animals were divided into four homogeneous groups of eleven animals each; one control group (CON) without extruded linseed and dietary supplements, and the diet of the other three experimental groups was enhanced with extruded linseed (L group), extruded linseed-verbascoside (LVB group), and extruded linseed-verbascoside-vitamin E (LVBE group). All animals individually received an isoenergetic diet, consisting of 700 g concentrated feed and meadow hay ad libitum. Body weight, body condition score, milk yield and milk qualitative parameters were assessed. LVB and LVBE groups resulted in a significant improvement (P<0·05) in milk yield due to the verbascoside supplementation. The extruded linseed supplementation L, LVB and LVBE groups produced a milk fat increase and a better milk fatty acid profile in terms of a higher monounsaturated fatty acid (MUFA), polyunsaturated fatty acid (PUFA) and conjugated linoleic acid (CLA) content and a reduced saturated fatty acid (SFA) content, a lower n-6/n-3 ratio and atherogenic and thrombogenic index. The dietary verbascoside supplementation in the LVB and LVBE group resulted in a better milk quality due to the low cholesterol level and higher vitamin A and E contents, in addition to an increased oxidative stability highlighted by the lower thiobarbituric acid reactive substances (TBARS) level. Thus, the addition of extruded linseed and verbascoside supplements improved milk yield and quality both from a chemical and nutritive point of view.

Effects of rapeseed and soybean oil dietary supplementation on bovine fat metabolism, fatty acid composition and cholesterol levels in milk

The main goal of this experiment was to study the effect of milk fat depression, induced by supplementing diet with plant oils, on the bovine fat metabolism, with special interest in cholesterol levels. For this purpose 39 cows were divided in three groups and fed different rations: a control group (C) without any oil supplementation and two groups with soybean oil (SO) or rapeseed oil (RO) added to the partial mixed ration (PMR). A decrease in milk fat percentage was observed in both oil feedings with a higher decrease of -1·14 % with SO than RO with -0·98 % compared with the physiological (-0·15 %) decline in the C group. There was no significant change in protein and lactose yield. The daily milk cholesterol yield was lower in both oil rations than in control ration, while the blood cholesterol level showed an opposite variation. The milk fatty acid pattern showed a highly significant decrease of over 10 % in the amount of saturated fatty acids (SFA) in both oil feedings and a highly significant increase in mono (MUFA) and poly (PUFA) unsaturated fatty acids, conjugated linoleic acids (CLA) included. The results of this experiment suggest that the feeding of oil supplements has a high impact on milk fat composition and its significance for human health, by decreasing fats with a potentially negative effect (SFA and cholesterol) while simultaneously increasing others with positive (MUFA, PUFA, CLA).

Effect of the metabolic environment at key stages of follicle development in cattle: focus on steroid biosynthesis

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of β-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.

Colorimetric detection of cholesterol with G-quadruplex-based DNAzymes and ABTS2-

A novel colorimetric method for detection of cholesterol was developed with hemin-G-quadruplex DNAzyme by transducing oxidation of cholesterol into the color change of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS(2-)). Oligonucleotide 5'-GTGGGTAGGGCGGGTTGG-3' (Oligo-1) formed G-quadruplex structure in the presence of K(+), it acted as a horseradish peroxidase (HRP) mimicking DNAzyme when binding hemin and catalyzed the oxidation of colorless ABTS(2-) to green ABTS(·-) by H(2)O(2), which was produced by the reaction of cholesterol and oxygen that catalyzed by cholesterol oxidase. Therefore, the oxidation of cholesterol could be transduced into the color change of ABTS(2-) by combining these two reactions. Under the optimum conditions, the absorbance was proportional to the concentration of cholesterol over the range of 1.0-30 μM, with a linear regression equation of A=0.362+0.0256C (C: μM, R=0.998) and a detection limit of 0.10 μM (3σ/slope). Moreover, the practicability of the assay in the detection of cholesterol in human serum was studied as well.