Milk Ingredients Research Articles

EXAMINATION OF THE COMPOSITION OF WHEY FROM MIXED CHEESE

In recent years, the ingredients of milk represent a functional food, because their use has a great effect on health. Whey is a byproduct of cheese production, which was previously considered waste. Whey proteins strengthen the immune system by helping the body produce the antioxidant glutathione, which protects against free radicals, pollution, toxins and infections. In this research we examine the composition of whey (minerals: Ca, K, Fe and P, total proteins and albumins) from mixed cheese from the "Ideal Shipka" dairy factory - Bitola. All parameters were determined spectrophotometrically, spectrophotometric, photometric - colorimetric and nephelometric methods were applied to prove the amount of certain components present in the whey composition. From the obtained results we can see that whey has the highest amount of total proteins, it contains 17.6 g/L, from which amount of albumen is 1,99 g/L. Of the minerals, the highest value was obtained for potassium 26,6 mmol/l, followed by calcium 9,47 mmol/l, amount of phosphorus was 9,39 mmol/l, while iron is found in a very small percentage 11,74 µmol/l. From the research we can conclude that whey contains a large percentage of total proteins, and of the minerals potassium. Thus, whey can be used as a dietary supplement for protein and potassium and it is attractive product for both the food and pharmaceutical industries and consumers.

Improved Anti-Oxidant and Anti-Bacterial Capacities of Skim Milk Fermented by Lactobacillus plantarum.

Milk, on account of its abundant protein content, is recognized as a vital source of bioactive substances. In this study, the bioactive ingredients in milk were obtained by a combination of protease hydrolysis and fermentation with Lactobacillus plantarum. The compositions of protease hydrolysate (PM) and fermentation supernatant (FM) were determined, and their anti-oxidant and anti-bacterial activities were evaluated. Using LC-MS/MS, the molecular weights and sequences of the peptides were characterized, among which a total of 25 bioactive peptides were identified. The DPPH radical scavenging results demonstrated that FM exhibited an enhanced anti-oxidant capacity compared to PM. The bacterial survival rate results revealed that FM had a remarkable anti-bacterial ability compared to PM. Additionally, the anti-bacterial component and potential anti-bacterial mechanisms were determined. The results of cytoplasmic membrane depolarization, cell membrane permeability, and morphological observation indicated that FM could interact with bacterial membranes to achieve its anti-bacterial effect. These findings suggested that FM, as a bioactive substance of natural origin, holds potential applications in the functional food, pharmaceutical, and cosmetic industries.

Multi-functional nanozyme-based colorimetric, fluorescence dual-mode assay for Salmonella typhimurium detection in milk.

Rapid and high-sensitive Salmonella detection in milk is important for preventing foodborne disease eruption. To overcome the influence of the complex ingredients in milk on the sensitive detection of Salmonella, a dual-signal reporter red fluorescence nanosphere (RNs)-Pt was designed by combining RNs and Pt nanoparticles. After being equipped with antibodies, the immune RNs-Pt (IRNs-Pt) provide an ultra-strong fluorescence signal when excited by UV light. With the assistance of the H2O2/TMB system, a visible color change appeared that was attributed to the strong peroxidase-like catalytic activity derived from Pt nanoparticles. The IRNs-Pt in conjunction with immune magnetic beads can realize that Salmonella typhimurium (S. typhi) was captured, labeled, and separated effectively from untreated reduced-fat pure milk samples. Under the optimal experimental conditions, with the assay, as low as 50 CFU S. typhi can be converted to detectable fluorescence and absorbance signals within 2 h, suggesting the feasibility of practical application of the assay. Meanwhile, dual-signal modes of quantitative detection were realized. For fluorescence signal detection(emission at 615 nm), the linear correlation between signal intensity and the concentration of S. typhi was Y = 83C-3321 (R2 = 0.9941), ranging from 103 to 105 CFU/mL, while for colorimetric detection(absorbamce at 450 nm), the relationship between signal intensity and the concentration of S. typhi was Y = 2.9logC-10.2 (R2 = 0.9875), ranging from 5 × 103 to 105 CFU/mL. For suspect food contamination by foodborne pathogens, this dual-mode signal readout assay is promising for achieving the aim of convenient preliminary screening and accurate quantification simultaneously.

Double-Tube Multiplex TaqMan Real-Time PCR for the Detection of Eight Animal-Derived Dairy Ingredients.

Milk and dairy products represent important sources of nutrition in our daily lives. The identification of species within dairy products holds importance for monitoring food adulteration and ensuring traceability. This study presented a method that integrated double-tube and duplex real-time polymerase chain reaction (PCR) with multiplex TaqMan probes to enable the high-throughput detection of animal-derived ingredients in milk and dairy products. The detection system utilized one pair of universal primers, two pairs of specific primers, and eight animal-derived specific probes for cow, buffalo, goat, sheep, camel, yak, horse, and donkey. These components were optimized within a double-tube and four-probe PCR multiplex system. The developed double-tube detection system could simultaneously identify the above eight targets with a detection limit of 10-0.1 pg/μL. Validation using simulated adulterated milk samples demonstrated a detection limit of 0.1%. The primary advantage of this method lies in the simplification of the multiplex quantitative real-time PCR (qPCR) system through the use of universal primers. This method provides an efficient approach for detecting ingredients in dairy products, providing powerful technical support for market supervision.

Milk: A Natural Guardian for the Gut Barrier.

The gut barrier plays an important role in health maintenance by preventing the invasion of dietary pathogens and toxins. Disruption of the gut barrier can cause severe intestinal inflammation. As a natural source, milk is enriched with many active constituents that contribute to numerous beneficial functions, including immune regulation. These components collectively serve as a shield for the gut barrier, protecting against various threats such as biological, chemical, mechanical, and immunological threats. This comprehensive review delves into the active ingredients in milk, encompassing casein, α-lactalbumin, β-lactoglobulin, lactoferrin, the milk fat globular membrane, lactose, transforming growth factor, and glycopeptides. The primary focus is to elucidate their impact on the integrity and function of the gut barrier. Furthermore, the implications of different processing methods of dairy products on the gut barrier protection are discussed. In conclusion, this study aimed to underscore the vital role of milk and dairy products in sustaining gut barrier health, potentially contributing to broader perspectives in nutritional sciences and public health.

The effect of alginate extract on the properties of brown rice (Oryza nivara) ice cream

The production of ice cream with the basic ingredients of brown rice milk is carried out to increase the consumption of antioxidants derived from brown rice (Oryza nivara). This is because the plant is less consumed due to its rough texture. The recent development of brown rice ice cream (BRICE) is intended to expand the use of the plant into a common commodity. Previous investigations have established that stabilizers are required in ice cream production, although only a few used natural stabilizers such as alginate. Therefore, this study aimed to determine the effect of adding the different concentrations of alginate from brown seaweed Laminaria sp. on the physical characteristic, namely melting power, viscosity, overrun, total dissolved solids, chemical properties, which include protein, fat, as well as antioxidant activity and hedonic level of BRICE. The concentration of alginate used was at 0.025%, 0.05%, 0.075%, and 0.1%, while the data collected were analyzed using analysis of variance (ANOVA) and Duncan’s test. The result showed that the addition of different alginate concentrations had a significant effect on the value of the parameters observed.

Detection of Adulterant Residues in UHT Milk Products using ATR-FTIR Spectroscopy

Milk adulteration has been done to gain economic benefit by which the quality of milk is purposely compromised either by combining or substituting important ingredients of milk with adulterants. The objectives of this study were to determine the milk quality parameters of adulterated and unadulterated milk products through quality analysis and to investigate the ATR-FTIR spectroscopy technique in detection of adulterant residues in milk products. UHT milk samples were used with three common adulterants (melamine, formalin, anionic detergent) in five different concentrations (0.2%, 0.8%, 1.2%, 1.5% and 2.0%). Quality analysis was done on unadulterated milk and adulterated milk samples. Results showed that there were no significant differences between them. Thus, ATR-FTIR spectroscopic analysis was used for the qualification of adulterants in the wavenumber range of 4000 to 500. These results show the potential of FTIR spectroscopy as a rapid and sensitive technique for the detection of adulterant residues in UHT milk products.

Human milk-derived versus bovine milk-derived fortifier use in very low birth weight infants: growth and vitamin D status.

Human milk-derived fortifier (HMDF) coupled with human milk feeding in extremely premature infants reduces the adverse outcome risks of early exposure to bovine milk ingredients but may not provide enough nutrients for adequate catch-up growth compared with bovine milk-derived fortifier (BMDF). This study aims to compare HMDF and BMDF effects on growth parameters and serum 25-hydroxy vitamin D (25OHD) levels in preterm very low birth weight (VLBW) infants during the first 8 weeks of life. We present a retrospective chart review of inpatient VLBW infants with birth weight <1,500 g and gestational age <32 completed weeks who received either their mother's milk or donor breast human milk fortified with HMDF or BMDF for the first 8 weeks. Weight, head circumference, length gain, and 25OHD level were calculated at 4 and 8 weeks of age. A total of 139 VLBW infants (91 HMDF + 48 BMDF) received fortified human milk without any supplemental premature formula from birth to 4 weeks of age, of whom 44 (37 HMDF + 7 BMDF) continued until 8 weeks of age. There was no statistically significant difference in the growth parameters between the two groups at 4 and 8 weeks of age. Serum 25OHD level in the HMDF group was significantly higher compared with that in the BMDF group at 4 weeks of age despite receiving lower vitamin D supplementation. Similar gain in growth parameters in HMDF and BMDF groups at 4 and 8 weeks of age was observed, suggesting that HMDF provides adequate nutrients for growth in VLBW infants. A higher 25OHD level in HMDF may suggest better absorption.

Early identification of cow’s milk protein allergy in infants in Kirkuk, Iraq, using milk-related symptom scores

Abstract Background: Milk is related to many gastrointestinal disorders from the cradle to the grave due to the many milk ingredients that can trigger gastrointestinal discomfort and disorders. Cow’s milk protein allergy (CMPA) is the most common food allergy, especially in infancy and childhood, which may persist into adulthood. Objectives: The aim of this study was to evaluate the effect of cow’s milk protein allergy (CMPA) in infants in its early identification using CMPA scoring system. Materials and Methods: We carried out an observational study at Azadi teaching Children’s Hospital’s pediatric gastrointestinal clinic from March to December 2021. Children seen in our pediatric GI clinic between the ages of 1 and 12 months were included. Infants with suspected CMPA were evaluated by cow’s milk-related symptom score (CoMiSS) tool. An allergic reaction, a gastrointestinal, respiratory, or dermatologic presentation, excluding an acute infectious disease, and at least one of the following conditions were required for a diagnosis of suspected CMPA. All participating doctors received the required training on CoMiSS, the oral challenge test procedure, and CMPA diagnosis and treatment guidelines before subject recruitment. Results: In this study, most of studied infants were men, and no significant difference between CMPA and non-CMPA infants regarding sex, age, and weight was found. In this study, 17.85% of infants with CMPA score suffered from occult blood in their fecal samples compared with 11.15% of non-CMPA infants (P &lt; 0.05). In this study, most of infants with CMPA have score 12, and the mean was 13.65 and the maximum value was 18. Conclusions: The CMPA score system provides primary healthcare clinicians with a simple, fast, and easy-to-use awareness tool for cow’s milk-related symptoms.

A Critical Review on the Role of Camel Milk in Multiple Health Outcomes

Camel milk has been demonstrated to be effective in treating a broad range of illnesses. Camel’s milk is regarded to have therapeutic properties because of its unique composition. Some people consider camel milk to be a precious commodity. White camel milk is made by combining fat and water. Several clinical studies have shown that camel’s milk is effective in treating a broad variety of diseases, including chronic ones. Most of the medicinal advantages of camel milk are included in this study. Camel Milk ingredients and qualities are similar to those found in mother’s milk, making it superior than cow’s milk. Insulin-like and protective proteins are found in abundance, along with lactose, which is the primary carbohydrate. It has anti-tumor qualities, and the robust immune system components assist combat disorders, including diabetes, autism, and diarrhea. It has been used by Nomads and Bedouins (Arabian tribals) for millennia because of these properties. The main objective of this review article is to demonstrate its various pharmacological roles. Camel’s milk is regarded as a vast medicinal property, as it contains a unique composition of bioactive moieties like lactose, proteins (Lactoferrin, Lactoperoxidase, Insulin, Casein), vitamins (A, B1, B2, C, D, E), minerals (Calcium, phosphorus, magnesium, iron, zinc and copper) carbohydrates etc. Most of the medicinal advantages of camel milk are covered in this paper, like its role in the management of autism, Crohn’s disease, allergic conditions, Hepatitis B and C, as antiviral and antibacterial agent. Hence, this study was planned to collect the updated latest information regarding use of camel’s milk, which will be very beneficial in the field of medicines and managing various ailments for the benefit of mankind.

Effects of Hemp Seed on the Production, Fatty Acid Profile, and Antioxidant Capacity of Milk from Goats Fed Hay or a Mixed Shrubs-Grass Rangeland.

The research objective was to evaluate the effect of dietary incorporation of hemp seeds in goats fed with hay or mixed shrubs-grass rangeland on the production, FA profile and health-related lipid indices, antioxidant content and total antioxidant capacity of milk, with the purpose to increase the content of beneficial ingredients in milk and to improve its functional activity. Forty indigenous Carpathian goats were allocated into two groups according to the type of basic forage in their diet: hay (H) or mixed shrubs-grass rangeland (SG); each of them was further divided into two subgroups according to the presence of Hs in the concentrate mixture (250 g/kg) or not. Milk production was determined, and milk samples were collected and analyzed for fat, protein, lactose, and cholesterol content, as well as FA profile, lipophilic antioxidant content (α-tocopherol and retinol), and milk TAC. SG goats gave less milk (p < 0.01) but with higher milk fat (p < 0.001) and lower cholesterol content (p < 0.01) than H goats, while milk protein and lactose contents were not affected. Supplementing the diet with Hs caused a significant increase in milk production (p < 0.05) and milk fat content (p < 0.001) and a decrease in cholesterol content (p < 0.05). Grazing compared to indoor feeding but also supplementing the diet with Hs had the effect of decreasing the proportion of SFAs and increasing the concentrations of polyunsaturated FA (PUFA) in goat milk fat (p < 0.01). Fats in the milk of SG goats compared to H, but also in those supplemented with Hs, showed significantly higher proportions of vaccenic acid (VA), rumenic acid (CLA c-9,t-11) and omega-3 FA (α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosapentaenoic acid (DPA)) which are considered healthy for consumers. The feeding system based on SG and the diet supplementation with Hs ensured the best nutritional and functional quality of milk, confirmed by the FA profile, antioxidant content, and by the value of health-related lipid indices (n-6/n-3 FA ratio and hypo-/hypercholesterolemia, atherogenic index (AI), thrombogenic index (TI), and health promotion index (HPI)). The results of our work will be useful for the development of optimal nutritional strategies that improve the FA profile and the antioxidants content in goat milk, with beneficial effects on human health.

Молочные ингредиенты – будущее молочной индустрии

The new area of milk processing is discussed in the article – the functional technological ingredient obtaining. Much attention is paid to protein components, their composition, physical and chemical properties and fields of application.

SIGNIFICANCE OF GENETIC CASEIN POLYMORPHISM IN ANIMAL HUSBANDRY

: Milk proteins are a rich source of peptides which are bioactive. Beta-casomorphin-7 ( BCM-7) is produced by successive proteolytic ingestion of beta- casein variants A1 and B, while not observed in A2 variant. The large amount of proteins in bovine’s milk are caseins, which consist of four categories ( αs1, αs2, β, and κ) encrypted by corresponding genes ( CSN1S1, CSN1S2, CSN2, and CSN3, respectively). Ingestion of A1 beta-casein showed the way for the emergence of beta-casomorphin-7 (BCM-7), a peptide that has been proposed to be a major cause of various human hazards.The relative profuseness of proline, methionine, and α-lactose were the highest in A2 variant of β-casein, while glycine, citric acid, choline, and cAMP (cyclic Adenosine Monophosphate) exhibited the highest abundance in A1 variant. These results thus come up with novel insights into the effect of casein variants, further expediting research into the biogenesis of milk ingredients and the prospective physiological activity of milk correlated with variants of β-casein.

Production of fermented milk analogs using subcritical water extraction of rice by-products and investigation of its physicochemical, microbial, rheological, and sensory properties.

Rice milling by-products extract and Persian grape syrup (Persian grape molasses), as the proper alternatives for milk ingredients and sucrose, respectively, can be considered a promising way to produce functional milk analogs. In this study, we studied the production of rice milling by-product extracts via the subcritical water extraction method, as a green method. The optimum extract was then fermented by Lactobacillus casei and Lactobacillus plantarum, and the different physicochemical, sensory, and rheological properties and the viability of these lactic acid bacteria were assessed during fermentation and certain intervals of 28-day storage. Considering rheological properties, the optimum rice milling by-product extract was recognized based on DOE analysis and the rheological curves of fermented drinks and Persian grape molasses were fitted by Herschel-Bulkley and Bingham models, respectively. The extract and also milk analog had excellent fitness with Herschel-Bulkley model, and this fermented milk analog showed a drop in the consistency index, flow behavior, and yield stress during the 28-day storage. According to the results, the viable cell count of Lactobacillus plantarum and Lactobacillus casei remained at 106-108 colony forming unit/mL after 28-day storage, which showed a combination of rice milling by-product ingredients and inulin had a positive effect on the survival rate of lactic acid bacteria. An increase in values of total phenolic compounds, as well as antioxidant activity observed during fermentation; however, these compounds dropped considerably during storage as a result of degradation and interaction with other compounds. Moreover, in terms of sensory evaluation, Lactobacillus plantarum drinks provided the highest overall acceptability among other samples on the 28th day.

Milk Yield and Composition, Technological Properties and Homeostasis Indices at Different Lactation Stages and Parities of Two Polish Dairy Goat Breeds

Abstract The purpose of the research was to determine the effect of breed, lactation number, and lactation stage on milk efficiency and goat milk ingredients, these being indicators of milk technological parameters and homeostasis disturbances. Goat breed and number of lactation affected energy-corrected milk, value-corrected milk yield, fat corrected milk, protein, casein, lactose contents and free fatty acids. Additionally, differences in non-fat solids and urea contents were found between two Polish common dairy breeds White Improved (PWI) and Fawn Improved (PFI) goats. Moreover, parity affected milk yield, its acidity and somatic cell count (SCC). Milk yield and milk components were found to vary according to lactation stage. At the beginning of lactation, milk is richer in ingredients which have effect on cheese and yoghurt production. All the goats undergo similar changes related to the lactation stage that is at the same time and this can affect the yield and quality of the curd. In production focused on liquid milk, the age structure of the herd should be properly managed, as the goats in their third lactation or above have higher milk yields, regardless of breed. For cheese production, the PWI breed would be more suitable than PFI as the PWI goat milk contains less SCC and more components essential for milk processing, including caseins.

Determination and Risk Assessment of Flavor Components in Flavored Milk.

This study aimed to determine chemical composition and assess exposure in flavored milk among Chinese residents, based on risk assessment methodologies of acceptable daily intake (ADI) and toxicological concern threshold (TTC). Esters (32.17%), alcohols (11.19%), olefins (9.09%), aldehydes (8.39%), and ketones (7.34%) comprised the majority of the flavoring samples. Methyl palmitate (90.91%), ethyl butyrate (81.82%), and dipentene (81.82%) had the highest detection rates in flavor samples. This study screened fifteen flavor components of concern and discovered that 2,3,5-trimethylpyrazine, furfural, benzaldehyde, and benzenemethanol were detected in 100% of flavored milk samples. Benzenemethanol was found in the highest concentration (14,995.44 μg kg-1). The risk assessment results revealed that there was no risk for Chinese residents in consuming flavored milk, and the maximum per capita daily consumption of 2,3,5-trimethylpyrazine, furfural, and benzenemethanol were 226.208 g, 140.610 g, and 120.036 g, respectively. This study could provide guidelines for amounts of flavor additive ingredients in milk.

Effect of Buffalo Breed on the Detailed Milk Composition in Guangxi, China.

Buffalo is the second source of milk in the world, and its milk is rich in nutritive components. It is well-known that breed influences milk composition. This work aimed to compare the detailed milk composition of three buffalo breeds (Murrah, Nili-Ravi, and Mediterranean) housed under the same environmental conditions. Mediterranean buffalo milk showed a significantly higher content of fat, protein, and some fatty acids. Moreover, the milk from the Mediterranean breed was characterized by the highest content of sphingomyelin (SM), cholesterol, and lanosterol. However, the Murrah buffalo milk contained the highest amount of total unsaturated fatty acids, phosphatidylinositol, and whey proteins. Furthermore, the Nili-Ravi buffalo milk was characterized by the highest content of total saturated fatty acids, phosphatidylglycerol, squalene, lathosterol, stigmasterol, beta-sitosterol, and casein fractions. Nevertheless, the lactose and amino acid profiles of the milk remained almost similar across the three buffalo breeds. The generated results in this study enable a comprehensive understanding of the milk constituent variability that is linked to buffalo breeds, which may support the acquirement of essential scientific knowledge on milk ingredient-processing interactions that will offer a foundation of knowledge for Chinese dairy processors in terms of milk processability and innovation.

Impact of protein-providing milk ingredients on volatile compounds, microstructure, microbiology and physicochemical characteristics of yogurts

The impact of skim milk (SM), demineralized whey (DW), whey protein concentrate (WPC40-WPC80), isolated (WPI) and hydrolyzed (WPH) on different parameters of yogurts have been evaluated using SLB95 and Yoflex starters. Addition of whey proteins shortened the fermentation time in yogurts with the exception of WPH, which extended it and presented the highest titratable acidity. WPH increased the Lactobacillus and decreased Streptococcus population in yogurts with SLB95 starter. WPI and WPC80 increased water-holding capacity. WPI and WPC80 yogurts exhibited larger aggregates, compared to the rest ingredients, and be bigger with the SLB95 starter. The volatile compounds differ, though not greatly, among yogurts.

Preventative and therapeutic potential of animal milk components against COVID-19: A comprehensive review.

The global pandemic of COVID-19 is considered one of the most catastrophic events on earth. During the pandemic, food ingredients may play crucial roles in preventing infectious diseases and sustaining people's general health and well-being. Animal milk acts as a super food since it has the capacity to minimize the occurrence of viral infections due to inherent antiviral properties of its ingredients. SARS-CoV-2 virus infection can be prevented by immune-enhancing and antiviral properties of caseins, α-lactalbumin, β-lactoglobulin, mucin, lactoferrin, lysozyme, lactoperoxidase, oligosaccharides, glycosaminoglycans, and glycerol monolaurate. Some of the milk proteins (i.e., lactoferrin) may work synergistically with antiviral medications (e.g., remdesivir), and enhance the effectiveness of treatment in this disease. Cytokine storm during COVID-19 can be managed by casein hydrolyzates, lactoferrin, lysozyme, and lactoperoxidase. Thrombus formation can be prevented by casoplatelins as these can inhibit human platelet aggregation. Milk vitamins (i.e., A, D, E, and B complexes) and minerals (i.e., Ca, P, Mg, Zn, and Se) can have significantly positive effects on boosting the immunity and health status of individuals. In addition, certain vitamins and minerals can also act as antioxidants, anti-inflammatory, and antivirals. Thus, the overall effect of milk might be a result of synergistic antiviral effects and host immunomodulator activities from multiple components. Due to multiple overlapping functions of milk ingredients, they can play vital and synergistic roles in prevention as well as supportive agents during principle therapy of COVID-19.

Taste Responses and Ingestive Behaviors to Ingredients of Fermented Milk in Mice.

Fermented milk is consumed worldwide because of its nutritious and healthful qualities. Although it is somewhat sour, causing some to dislike it, few studies have examined taste aspects of its ingredients. Wild-type mice and T1R3-GFP-KO mice lacking sweet/umami receptors were tested with various taste components (sucrose, galactose, lactose, galacto-oligosaccharides, fructo-oligosaccharides, l- and d-lactic acid) using 48 h two-bottle tests and short-term lick tests. d-lactic acid levels were measured after the ingestion of d- or; l-lactic acid or water to evaluate d-lactic acidosis. In wild-type mice, for the sweet ingredients the number of licks increased in a concentration-dependent manner, but avoidance was observed at higher concentrations in 48 h two-bottle tests; the sour ingredients d- and l-lactic acid showed concentration-dependent decreases in preference in both short- and long-term tests. In 48 h two-bottle tests comparing d- and l-lactic acid, wild-type but not T1R3-GFP-KO mice showed higher drinking rates for l-lactic acid. d-lactic acidosis did not occur and thus did not contribute to this preference. These results suggest that intake in short-term lick tests varied by preference for each ingredient, whereas intake variation in long-term lick tests reflects postingestive effects. l-lactic acid may have some palatable taste in addition to sour taste.