Beetroot and Sweet Potato Prebiotics Push Probiotic Milk to 800 Million Bacteria Per mL

Getting live bacteria to survive inside a dairy product long enough to benefit the consumer is harder than it sounds. Fermented milk starts with a healthy culture, but heat, acidity, and competition from other microbes can chip away at that count before the product even reaches a shelf. A new study published in Jurnal Sains Natural by researcher S Nurmala explores whether extracts from two common vegetables, beetroot and yellow sweet potato, can act as prebiotics to feed and sustain lactic acid bacteria (LAB) through the fermentation process. The results are preliminary but point toward a practical, low-cost approach to improving probiotic dairy products.

Fermented Milk Spiked with Beetroot and Sweet Potato Reaches 800 Million Bacteria Per mL

The best-performing formula in this study, labeled F6, combined 4% beetroot extract with 6% yellow sweet potato extract added to a standard fresh and skim milk base. After 18 hours of incubation at 40 to 45 degrees Celsius, F6 produced a LAB count of 8 x 10^8 colony-forming units per milliliter. That figure matters because regulatory and scientific consensus generally places the minimum effective probiotic dose at 1 x 10^6 CFU/mL, meaning F6 exceeded that threshold by roughly 800 times. The product also met Indonesian, International Dairy Federation, and Food Standards Australia New Zealand pH standards, coming in at 3.984 against a maximum allowable pH of 4.5 to 4.6. No Coliform or Salmonella contamination was detected, and heavy metal readings (lead at 0.01 mg/kg, mercury below 0.005 mg/kg) both fell well under national limits.

Why Prebiotic Pairing Could Help Lactose-Intolerant Consumers and Gut Health

The broader appeal of this kind of formulation goes beyond raw bacteria counts. Fermented milk is already easier to digest for the roughly 65 percent of adults worldwide who have some degree of lactose intolerance, because LAB consume much of the lactose during fermentation. Adding prebiotics, the dietary carbohydrates that selectively feed beneficial microbes in the large intestine, is meant to extend that advantage. Research on root and tuber prebiotics and gut health has shown that resistant starches, inulin, and oligosaccharides from plants like sweet potato can meaningfully shift gut microbiota composition, which in turn influences metabolic and immune outcomes. Yellow sweet potato is notable here because it contains 25.1 g of carbohydrates per 100 g along with oligosaccharides that behave as natural prebiotics. Separately, studies on sweet potato prebiotic potential show that sweet potato purees can stimulate the growth of beneficial gut bacteria and short-chain fatty acid production in laboratory conditions. The broader benefits of lactic acid bacteria fermented products include immunomodulatory effects and protection against pathogens, making a well-formulated synbiotic dairy product, one that combines both probiotics and prebiotics, a potentially useful everyday food.

How Six Formulas Were Tested to Find the Optimal Prebiotic Ratio

Nurmala prepared prebiotic extracts by peeling, washing, grating, and pressing both vegetables, then pasteurizing the liquid. The milk base (fresh milk, skim milk, and sucrose) was also pasteurized at 80 to 90 degrees Celsius for 15 minutes to eliminate Coliform and Salmonella before a commercial starter culture called YOE was added aseptically. YOE contains two well-characterized bacteria: Lactobacillus bulgaricus, which produces lactic acid and aroma compounds like acetaldehyde and diacetyl, and Streptococcus thermophilus, which primarily drives acidity by lowering pH. Six formulas (F1 through F6) varied the ratio of beetroot to yellow sweet potato extract, and all were evaluated for LAB count using the Total Plate Count method, pH, contamination, heavy metals, proximate composition, and consumer preference through a hedonic (sensory rating) test. Research into lactofermented beetroot juice methodology has explored similar controlled fermentation approaches using specific probiotic strains, lending context to the fermentation design used here. For beetroot products with lactic acid bacteria, the literature consistently highlights beetroot's bioactive compounds as relevant to microbial quality, which helps frame why the researchers included it at all.

Beetroot's Antibacterial Compounds Create a Formulation Ceiling

One of the more counterintuitive findings was that increasing beetroot concentration alone did not steadily improve LAB counts. Formulas with higher proportions of beetroot relative to sweet potato tended to suppress bacterial growth. The likely culprit is beetroot's phenol and flavonoid content, measured in this study at 376.4 mg/g and 253.5 mg/g respectively. These compounds, while potentially beneficial for human health as antioxidants, are antibacterial at sufficient concentrations; they can damage bacterial cell walls, inhibit enzymes, and interfere with nucleic acid synthesis. This created a ceiling effect: too much beetroot, and the very compounds meant to enrich the product began undermining its probiotic core. The sweet spot turned out to be the 4% beetroot, 6% yellow sweet potato ratio of F6, where carbohydrate substrate from both sources fed the bacteria without overwhelming them with antimicrobial compounds.

Consumer Acceptance and the Aroma Problem Still Need Solving

The hedonic test showed that panelists generally preferred F6 overall, but the formula drew lower scores specifically for aroma. The dominant smell of yellow sweet potato was noticeable and divisive enough that the aroma category registered a statistically significant difference from other formulas. This is a practical obstacle: a probiotic milk product that meets every microbiological and nutritional benchmark still needs to be something people want to drink. Proximate analysis confirmed that F6's nutritional profile is sound, with 81.46% water content, 2.36% protein, and 3.48% fat, all meeting Indonesian national standards (SNI minimum: 1.0% protein, 2.7% fat). Future work, the study suggests, should focus on flavoring strategies that preserve the prebiotic carbohydrate content and LAB viability while softening the vegetable aroma enough to make the product commercially viable. Whether that means adjusting the ratio further, adding natural flavor masking agents, or changing the extraction method remains an open question.

Evidence rating

INVESTIGATIONAL — 63/100

Single experimental formulation study with no reported human or animal subjects — findings reflect in-vitro product development outcomes across six formula variants. The study cannot establish causal effects on human health, and no independent replication exists. Results are preliminary and specific to the tested product formulation only.

References

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