The main materials used in dadih production are buffalo milk, bamboo tubes, and banana leaves. The buffalo milk generally contains higher total solids content compared to other mammals’ milk, especially due to the higher casein and fat content, which are responsible for the creamy, thick body, and custard-like consistency of dadih. The higher fat content of the milk results in softer texture and developed flavor of dadih.
Bamboo tubes are chosen as the containers during fermentation because they have hygroscopic properties to keep the product from whey separation, and the bitter taste of bamboo can prevent contamination against ants. Many types of bamboo used in dadih fermentation were reported, including bamboo ater (Gigantochloa atter), bamboo gombong (Gigantochloa verticillata), bamboo lengka tali (Gigantochloa hasskarliana), bamboo ampel (Bambusa vulgaris), and bamboo betung (Dendrocalamus asper). Among these bamboo types, the native Minang people prefer to use bamboo gombong. The number of indigenous microbes found on the inner surface of bamboo was 2.5 × 102–1.0 × 103 cfu/cm2, and acid-producing proteolytic bacteria were found to be in the majority, followed by yeast. The type of bamboo also affects the flavor of the resulting dadih. By analyzing the flavor, color, aroma, and texture in hedonic evaluation, the salad dressing from goat milk dadih fermented in bamboo ampel was significantly preferred (p < 0.05) compared to that in bamboo gombong, especially within 2 days of the fermentation process.
Banana leaves are commonly used to cover the bamboo tube during dadih fermentation. The purpose of using banana leaves is to create the facultative anaerobic condition which is optimum for the fermentation process, as well as to avoid unwanted contamination. However, depending on the region, not only banana leaves, but also taro leaves or plastics are used to cover the bamboo. To tie the cover, banana bark or rubber bands are used.
The traditional production process of dadih-
In West Sumatra, most buffaloes produce around 2 L of milk a day. After milking the buffalo, the raw buffalo milk (free from antibiotics) is directly filtered to reduce the physical contamination such as stones and grass. The filtered milk is then poured into the bamboo tube, covered with banana leaves, and tied with a rubber band or banana bark. The fermentation process occurs spontaneously at room temperature (28–30 °C) for 24 h or even 2–3 days. The indigenous LAB and proteases will perform the lactic acid fermentation as well as proteolytic activity to produce the dadih with a thick consistency, solid texture, smooth surface, and pleasant flavor. The fermentation by LAB is very important to reduce the contaminant by pathogens and spoiling bacteria, thus makes dadih safer to consume. The possible mechanisms are by producing the inhibitory metabolites, for example, the organic acids (mainly lactic acid) during the fermentation process, which then decreases the pH of the medium and pathogens cannot grow well by producing bacteriocins.
Dadih is similar to dahi from India, however, they have some differences. In dadih production, heat treatment is not applied to the raw buffalo milk, and no starter culture is added for fermentation. While in dahi production, the pasteurization process of raw buffalo or cow milk or a combination of both kinds of milk is applied before fermentation, and the back-slopping method (a small quantity of dahi from the previous lot is used as a starter culture of the next lot) is used. In comparison to yogurt, the fermentation time of dadih is longer (24 h up to 3 d) than yogurt (4 h). Furthermore, the mesophilic LAB is involved at 28–30 °C in dadih fermentation, while thermophilic LAB is involved at 45 °C in yogurt fermentation. The involvement of indigenous yeasts in dadih fermentation also differs the dadih from yogurt.
Maturation of Dadih-
Carbohydrate fermentation, proteolytic activity, and lipid metabolism contribute to the formation of the desired structure and flavor of dadih. In carbohydrate catabolism, LAB converts lactose into lactic acid by involving β-galactosidase and lactic acid fermentation. The resulting lactic acid decreases the pH value of buffalo milk and contributes to protein precipitation or coagulation of buffalo milk, so the curd or dadih is formed. Decreasing pH value from 6.92 (raw buffalo milk) to 4.65 after 2 days of dadih fermentation was observed. Through carbohydrate catabolism, small quantities of flavor compounds are also formed through the volatile fatty acids, ethanol, acetoin, acetic acid, butanone, diacetyl, and acetaldehyde. Lactic acid, as the major fermentation product, is produced by the homofermentative LAB, such as Lactobacilli, Lactococci, Pediococci, and Streptococci, while flavor formation is formed by heterofermentative LAB such as Levilactobacillus brevis, Limosilactobacillus fermentum, and Leuconostoc sp. Lactic acid formed by LAB contributes to the destabilization of casein micelles to form curd and gives the distinctive and characteristic sharp acidic taste of dadih. Moreover, dadih is safely consumed by people with lactose intolerance, as during dadih fermentation, the β-galactosidase activity and lactic acid fermentation can help the digestion of lactose.
The proteolytic system of LAB is complicated, especially in turning milk casein into free amino acids and peptides which are needed for LAB growth. However, the overall proteolytic system of LAB is very weak. To support LAB growth, raw buffalo milk possesses indigenous enzymes that may also contribute to making amino acids and peptides. Since heat is not applied during dadih production, the thermal breakdown of raw buffalo milk protein, denaturation, and coagulation of albumins and globulins will not occur. So, the degradation of protein will be catalyzed by bacterial or native proteases. The proteolytic activity from milk proteases, such as plasmin or proteases of bacterial origin, help in the thickening, gelation, and coagulation process of buffalo milk in dadih production.
The natural lipases in the raw buffalo milk may take part in lipid metabolism, while the insignificant amount of free fatty acids and volatile fatty acids are released by microbial contaminants of the buffalo milk. The high-fat content of buffalo milk (twice as high as cow milk) contributes to the creamy textures and various flavors in dadih.
Microbiota of Dadih-
In spontaneously fermented products, various types of microbiotas might be involved, including, but not limited to, LAB and yeasts. In dadih, the indigenous LAB of buffalo milk are the main group of microbes that are involved in dadih fermentation. The LAB will dominate and grow during the fermentation, decrease the pathogenic and spoilage bacteria, and develop the flavor of dadih. The total viable LAB count was in the range of 1.42 × 108–3.80 × 108 cfu/g. Various types of LAB can be found from one place to another in West Sumatra. Leuconostoc paramesenteroides, which produce acetic acid, diacetyl, and other volatiles as the aromatic compounds were reported as the predominant strains of LAB. Nuraida reported that Leuconostoc mesenteroides, Lactococcus lactis subsp. lactis, Levilactobacillus brevis, Lacticaseibacillus casei, Lactiplantibacillus plantarum subsp. plantarum, Enterococcus faecium, Limosilactobacillus fermentum, and Lacticaseibacillus rhamnosus were found in dadih from buffalo milk. The unhygienic process applied in dadih production becomes the possible reason, as Enterococci group bacteria, such as Enterococcus faecalis was also found in dadih. Furthermore, the types of fermentation (spontaneous and back-slopping) affect the diversity of LAB in dadih, as black-slopping fermentation results in greater diversity compared to spontaneous dadih fermentation. Bifidobacterium (18% of total microbiota composition) was found in non-pasteurized dadih from the Palupuh region, prepared using back-slopping method.
