The 2 positive-quality studies were conducted by Diaz-Lopez et al and El Khoury et al. In a CS study, Diaz-Lopez et al followed nondiabetic elderly subjects in a Mediterranean population and reported an inverse relationship between T2D cases and total low-fat dairy and yogurt consumption. Three neutral-quality studies , , reported a significant association between consumption of either yogurt or fermented milk and decreased risk of T2D, and 2 neutral-quality studies , reported an association between yogurt consumption, lower levels of glucose, lower levels of insulin, and less insulin resistance.
One neutral-quality study reported a nonsignificant outcome on the effect on diabetes risk with consumption of fermented milk products, Soedamah-Muthu et al evaluated the intake of fermented milk products in a subpopulation from the Whitehall II study and found it to be inversely associated with overall mortality, but not with diabetes. Overall, these studies indicate a significant correlation between fermented milk consumption and reduced risk for T2D. Four neutral-quality studies specifically evaluated metabolic syndrome.
One component of the 5 MetS criteria, central adiposity, was found to be significantly inversely associated with high yogurt consumption.
Kim and Kim 62 reported that for a cohort of men and women aged 40—69 years, consumption of 4 or more servings of yogurt per week was associated with a decreased risk for MetS.
Among a cohort of men and women aged 18—55 years, Cormier et al 94 reported that yogurt consumption led to an improved cardiometabolic risk profile. Overall, studies suggest yogurt consumption is strongly associated with risk reduction of metabolic syndrome and diabetes.
Seven included studies evaluated the impact of yogurt and cultured fermented milk on bone health — ; 1 study was an RCT, 3 were cohort studies, — and 3 were CS studies. All of the studies evaluated yogurt consumption or yogurt feeding and one of these used laban, a liquid-type yogurt. Five of the studies — , , reported a favorable outcome of yogurt consumption, and 2 studies , reported a neutral outcome.
Only one study, conducted by He et al, was positive quality; the other 6 studies , — were neutral quality. The treatment group reported improved nutrient intake, lower incidence of respiratory infections and diarrhea, greater height and weight gain, and greater bone mineral density.
In a CS study of an Iranian female adult population, AlQuaiz et al found an increased risk for low bone mineral density among those who did not drink laban yogurt drink. As part of the Framingham Offspring cohort study, Sahni et al found an association between yogurt consumption and increased bone density. No other dairy groups showed an association. Overall, the studies confirm the positive effect of the high nutrient content of yogurt on bone health.
Conclusions that may be drawn from this systematic review are that 1 a causal relationship exists between lactose digestion and tolerance and yogurt consumption, and 2 consistent associations exist between fermented milk consumption and reduced risk of breast and colorectal cancer, T2D, improved weight maintenance, and improved cardiovascular, bone, and GI health.
Further, an association exists between prostate cancer and dairy product consumption in general, with no difference between fermented and unfermented products. There exist several possible mechanisms for these findings. During fermentation, metabolic activity of microorganisms can alter the nutritive and bioactive properties of dairy products.
Thus, health-promoting properties of fermented milk products may be due, in part, to the biosynthesis or release of bioactive compounds resulting from the fermentation process, including bioactive peptides with antihypertensive, antimicrobial, antioxidative, and immune-modulatory activities.
The strongest evidence supporting the health benefits of fermented foods is for their ability to improve lactose digestion and tolerance. Multiple RCTs support this function and the physiological role of the beta-galactosidase enzyme produced by yogurt bacteria for in vivo hydrolysis of lactose during GI transit, resulting in improved lactose digestion and tolerance.
An important potential confounding factor in cohort and other correlation-based studies is that individuals with a propensity toward healthy diets may simply consume more fermented foods. Thus, it is critical that, when feasible, controlled and blinded studies be conducted with populations matched for age, gender, socioeconomic status, education, and other factors that may influence food consumption behavior.
Although the limitations of observational studies are well known including potential for bias and lack of causation , they can still provide valuable suggestions for improving public health.
Hence, distinguishing the health benefits of fermented vs nonfermented milk products is often difficult. Many of the studies cited in this review used milk products as controls. Thus, these studies are able to distinguish the specific effect of fermentation. In contrast, other studies utilized nonmilk controls, cannot distinguish between nutrient content and fermentation factors influencing the results.
In a review of dietary recommendation in 13 European Union member states, none mentioned yogurt as an alternative for people with lactose intolerance, despite an approved function claim in the European Union for live cultures in yogurt or fermented milk to aid with lactose digestion. Evidence described in this review suggests such recommendations are warranted. Authors R. They are solely responsible for its content. Danone North America did not provide concept, design, or approval of this manuscript.
Declaration of interests. Health benefits of fermented foods: microbiota and beyond. Curr Opin Biotechnol. Google Scholar.
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An increase in the total DM content, particularly the proportion of casein and whey proteins, will result in a firmer yoghurt coagulum, and the tendency to whey separation will then be reduced. The disaccharide sucrose, or a monosaccharide such as glucose, can be added alone, or in conjunction with fruit addition. To satisfy dieters, among whom diabetics are an important category, sweeteners should be used. A sweetener has no nutritive value, but tastes very sweet, even in very small doses.
Hydrophilic colloids can bind water. They increase the viscosity and help to prevent whey separation in yoghurt. The type of stabilizer and the rate at which it should be added must be determined experimentally by each manufacturer. The product may acquire a rubbery, hard consistency if the wrong stabilizer, or an excess of stabilizer, is used.
Correctly produced, natural yoghurt requires no addition of stabilizers, as a firm, fine gel with a high viscosity will occur naturally. Stabilizers can be used in fruit yoghurts and must be used in pasteurized and whipped yoghurt. Stabilizers 0. The air content of the milk used to make fermented milk products should be as low as possible. However, some admixture of air is unavoidable if the MSNF content is increased by addition of milk powder.
If this is done, the milk should be deaerated as part of the subsequent processing. Zoom Fig The main motives for homogenizing milk intended for cultured milk production are to prevent creaming during the incubation period and to assure uniform distribution of the milk fat.
Homogenization also improves the stability and consistency of fermented milks, even those with low fat contents. Table Figure The viscosity of full-stream homogenized milk runs parallel to the homogenization pressure, regardless of whether it has been subjected to ordinary heat treatment or not.
The table also shows that high-temperature heat treatment makes the product more viscous. Homogenization is frequently utilized even in production of low-fat cultured milks. For certain recipes these higher parameters have a positive influence on both viscosity and stability. The question of single- or double-stage homogenization is sometimes discussed. Generally speaking, this is a matter of the design of the homogenization system and of the homogenizer head in particular.
UHT treatment and sterilization of milk intended for culturing do not, however, have the same favourable influence on viscosity, for reasons not yet fully understood. Culture laboratories today produce a wide range of customized yoghurt cultures. Dairies can choose branded yoghurt cultures or mix cultures themselves to get their own requirements for the final yoghurt. Some cultures will give the final yoghurt different mouth thickness and gel firmness. Other cultures that influence fermentation time and post acidification.
Cultures are also adapted to the type of yoghurt that should be produced e. In earlier times it was common that dairies bought a mother culture from a culture laboratory. The dairy then propagated the culture itself in water baths and bulk starter tanks to get enough for the yoghurt production.
This system is rarely used today. It is so much easier and safer to use the highly concentrated cultures produced by the culture company. These cultures are distributed deep frozen or freeze dried. The coagulum formed during fermentation is sensitive to mechanical treatment.
This makes the selection and dimensioning of pipes, valves, pumps, coolers, etc. The pre-treatment of the milk is the same, regardless of whether set or stirred yoghurt is to be produced. It includes standardization of the fat and DM contents, homogenization and heat treatment. The milk storage tanks, from which the milk is pumped to the process line, are not shown in the figure.
It is assumed that the milk has been standardized to the required fat content and pre-pasteurized before entering the line. In the example, standardization of the DM content takes place by adding milk powder or protein powder. The milk, increased in DM by adding milk powder, should preferably be deaerated to reduce the risk of whey separation in the final yoghurt.
Any additives, such as stabilizers, vitamins, etc. From the pre-heater the milk is deaerated in a vacuum vessel. The deaerated milk continues to the homogenizer 4 and is homogenized at a pressure of approx.
The milk then flows to a holding section dimensioned for a holding time of five minutes. The tubular holding section shown in Figure When the yoghurt milk has been pre-treated and cooled to inoculation temperature, the procedure for further treatment depends on whether set, stirred, drink, frozen or concentrated yoghurt is to be produced.
The block diagrams in Figures The quality of the yoghurt in terms of texture and flavour depends on the design of the plant, the treatment of the milk and the treatment of the product.
Modern plants are designed to satisfy demands for high production, continuous treatment and high quality. The level of automation varies, and complete CIP systems are normally integrated into the plants.
The level of automation is usually high in large-scale production. Excessive mechanical treatment of the product must be avoided, as it may cause product defects such as thin consistency and whey separation. The total amount of treatment to which the product is subjected must be taken into consideration when the plant is designed. The choice of suitable equipment and the matching and optimization of the plant are consequently a question of achieving a suitable balance between cost and quality.
In modern plants, stirred and set types of yoghurt are often produced concurrently. In the production of set yoghurt, the product flow is continuously controlled from the point where the milk is accepted in the pre-treatment section to the packaging of the product. In the production of stirred yoghurt, the pre-treatment of the milk is continuous up to the point at which it is pumped into the incubation tanks, to which the culture is added.
The continuity is interrupted by the time-consuming incubation, which must be free from any physical disturbance. A typical plant for continuous production of a relatively large volume of stirred yoghurt is shown in Figure The pre-treated milk, cooled to incubation temperature, is pumped to the incubation tanks 7 in succession.
Simultaneously, freeze dried or deep frozen culture is dosed into the milk stream. After a tank has been filled, agitation commences and continues for a short time to assure uniform distribution of the starter culture. The incubation tanks are insulated, to ensure that the temperature remains constant during the incubation period. The tanks can be fitted with pH meters to check the development of acidity. The relative short incubation time indicates that the multiplication generation period is fast.
For typical yoghurt bacteria, the generation period is some 20 — 30 minutes. Many parameters in the line are responsible for the final quality. In the final stage of incubation, when the required pH normally about 4. This temporarily stops any further increase in acidity. At the same time, the coagulum must be subjected to gentle mechanical treatment, so that the final product will have the correct consistency. In some cases a strainer or a structurizing valve is built into the line, prior to the cooler, in order to optimize the yoghurt structure and appearance.
Cooling takes place in a plate heat exchanger 8 , which is designed to give a gentle mechanical treatment of the product. The capacities of pump and cooler are often dimensioned to empty a tank in about 30 minutes in order to maintain a uniform product quality. However, some cultures are specially adapted to stop when reaching pH e. The cooled yoghurt is pumped to buffer tanks 9 before being routed to the filling machine s Fruit and various flavourings can be added 10 to the yoghurt when it is transferred from the buffer tanks to the filling machines.
This is done continuously with a variable-speed metering pump, which feeds the ingredients into the yoghurt in the fruit-blending unit shown in Figure The blending unit is static and hygienically designed to guarantee that the fruit is thoroughly mixed into the yoghurt.
The fruit metering pump and the yoghurt feed pump operate synchronously. The fruit should be as homogeneous as possible. A thickener in the form of pectin can be added. The proportion of pectin is hardly ever higher than 0. Proper heat treatment is an extremely important stage in the pre-treatment of fruit additives.
Scraped-surface heat exchangers, tubular heat exchangers or tanks with scraper units, can be used for adequate pasteurization of whole berries or fruit with solid particles. The temperature programme should be such that all vegetative microorganisms are inactivated without impairing the taste and texture of the fruit. Continuous production, with rapid heating and cooling, is therefore important with regard to product quality and economic aspects.
Following the heat treatment, it is important that the fruit is packed in sterilized containers under aseptic conditions. Deterioration of cultured milk products is too often caused by reinfection from inadequately treated fruit. Various types of filling machines are used to pack yoghurt.
The sizes of the packages vary from one market to another. In general, the total packing capacity should match the capacity of the pasteurization plant, so as to obtain optimal running conditions for the plant as a whole. As mentioned, the plant design is one important factor affecting the quality of the yoghurt and, of course, all other cultured products.
Curve A represents the ideal situation, when all operations that influence the structure and viscosity are optimized. It is inevitable that the product will become less viscous while being treated, since yoghurt belongs to the class of products with thixotropic flow behaviour. However, if all parameters and equipment are fully optimized, the viscosity will be almost fully regenerated, and the likelihood of syneresis occurring will be minimized. Curve B shows the result when the product has been maltreated on its way from the incubation tank up to packaging and cold storage.
If the yoghurt coagulum has been treated too hard, the viscosity will be too low, resulting in a liquid product with high risk for whey separation. In order to reduce installation costs, it is possible to use the same plant for production of both stirred and set yoghurt. The pre-treatment of the milk intended for either product is identical up to cooling down to incubation temperature.
The starter is metered into the stream of milk as it is pumped from an intermediate storage tank to the filling machine. Set yoghurt is produced by adding culture to pasteurized and cooled milk. Prior to the filling machine the mix of milk and culture is heated to exact fermentation temperature. Aroma may be added in line. The packed mixture is transported to an incubation room where the coagulation is made.
When ready, the set-type yoghurt is then cooled in a cooling tunnel. The most frequently used system for production of set yoghurt is illustrated in Figure This system offers flexibility in production planning, because it is not necessary to match pre-treatment capacity to packing capacity. Following culture inoculation and thorough stirring, the milk is ready to be heated in-line 2 to exact incubation temperature, before being packed 4 in containers. Flavouring can be continuously metered into the milk stream prior to the filling machine.
If fruit or additives with particles are added these have to be dosed into the packages or cups first before they are filled with inoculated milk. It is, however, important to remember that additives with low pH have a negative influence on fermentation. Following packaging the packages, after crating and palletizing, are trucked into either of two systems for incubation and subsequent cooling, viz.
The crates are normally stacked on pallets, which are then trucked into the incubation room. This ensures uniform quality, provided that the temperature is accurately controlled. When the empirically determined optimum pH typically 4. Cooling efficiency depends on the size of the individual package, the design and material of the packages, the depth of the crate stack, the spacing between individual packages in each crate, and the design of the crates.
A smaller, free cross-section will require higher airflows, which also means higher energy consumption. The pallets crates are stationary during incubation. In a typical incubation period of 3 — 3. The cooling capacity should be adequate to achieve the above-mentioned temperature programme. As a guide, the total cooling time is about 65 — 70 minutes for small packages 0. A low-viscosity drinkable yoghurt, normally with a low fat content, is popular in many countries.
The composition can be the same as for stirred yoghurt but can also be reduced in DM by e. The yoghurt intended for production of drinking yoghurt is produced in the ordinary way with fermentation in tanks.
In order to get a stable drinking yoghurt without sedimentation, a stabilizer commonly pectin but also modified starch or CMC are used should be added to the product before cooling.
The yoghurt with added pectin is homogenized prior to cooling to get optimal stabilizing effect. Shelf life of a fermented milk product is dependent on a number of visible and organoleptical factors like whey separation, changes in viscosity, structure, colour, acidity and aroma.
It is of course also dependent on bacteriological defects. Because of the tendency towards larger and more centralized production units, the markets are becoming geographically larger and transport distances longer.
In some cases, the sales district may be so large that only one delivery per week is economically justifiable. This, in turn, necessitates methods which extend the shelf life of the product beyond normal.
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