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Agglutination behavior of mesophilic starter cultures as a function of proteolysis
1Department of Nutrition and Food Science, Faculty of Agriculture, University of Jordan, Amman, Jordan. Ibrah009@tc.umn.edu
Abstract:
Seven mesophilic starter cultures were grown separately in sterilized skim milk for 8 h at 25 degrees C. At the end of the incubation period, samples were analyzed for agglutination behavior by using microscopic examination. Samples were also assayed for proteolytic activity by the spectrophotometric o-phthaldialdehyde (OPA) and trinitrobenzenesulfonic acid (TNBS) methods. This experiment was replicated three times in a randomized block design. Microscopic examination showed that some cultures existed as single cells, diplococci, or short chains; other cultures tended to form long chains. Short-chain-forming cultures had high proteolytic activities, whereas long-chain-forming cultures had low proteolytic activities as measured by the TNBS and OPA methods. Proteolysis measured by both methods ranked starter cultures in the same order (R2 = 0.82). Low detectability values (obtained by dividing the standard error of the sample estimate for each method by its slope ratio) for OPA and TNBS methods indicated that the two assays do not differ significantly (P > 0.05).
Insights
Starter culture morphology impacts proteolytic activity. Short-chain cultures exhibit high proteolysis, while long-chain cultures show low activity, as confirmed by spectrophotometric assays.
Area of Science:
- Dairy Microbiology
- Enzymology
Background:
- Mesophilic starter cultures are crucial in dairy fermentation.
- Understanding starter culture behavior, including cell morphology and proteolytic activity, is vital for optimizing dairy product quality.
Purpose of the Study:
- To investigate the relationship between the cell chain length of mesophilic starter cultures and their proteolytic activity.
- To compare the efficacy of spectrophotometric o-phthaldialdehyde (OPA) and trinitrobenzenesulfonic acid (TNBS) methods in quantifying proteolytic activity.
Main Methods:
- Seven mesophilic starter cultures were incubated in skim milk for 8 hours at 25°C.
- Agglutination behavior was assessed via microscopic examination.
- Proteolytic activity was quantified using the o-phthaldialdehyde (OPA) and trinitrobenzenesulfonic acid (TNBS) spectrophotometric methods.
- Experiments were replicated three times using a randomized block design.
Main Results:
- Microscopic examination revealed variations in culture morphology, forming single cells, diplococci, short chains, or long chains.
- A significant correlation was observed: short-chain-forming cultures displayed high proteolytic activity, whereas long-chain-forming cultures exhibited low activity.
- Both OPA and TNBS methods provided consistent rankings of starter cultures' proteolytic activity (R² = 0.82).
- Low detectability values indicated no significant difference between the OPA and TNBS assays (P > 0.05).
Conclusions:
- Starter culture morphology, specifically cell chain formation, is a reliable indicator of proteolytic activity.
- The OPA and TNBS methods are comparable and effective for measuring proteolytic activity in starter cultures.
- These findings contribute to a better understanding of starter culture performance in dairy fermentations.