Q.25 In a batch culture, the specific rate of substrate utilization is
0.25 g (g cell mass)−1 h−1 and specific rate
of product formation is 0.215 g (g cell mass)−1 h−1.
Calculate the yield of product from the substrate (Yp/s).
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Batch Culture Yp/s Calculation: 0.25 & 0.215 Rates Yield 0.86 g/g | Biotech Explained
The yield of product from substrate, denoted as Yp/s, measures the efficiency of product formation relative to substrate consumption in microbial batch cultures. For the given rates—specific substrate utilization of 0.25 g substrate per g cell mass per hour−1 and specific product formation of 0.215 g product per g cell mass per hour−1—Yp/s calculates to 0.86 g product per g substrate. This value indicates that 86% of consumed substrate converts to product under these conditions.
Yp/s Definition
Yp/s quantifies grams of product formed per gram of substrate utilized, a key metric in bioprocess engineering for fermentation optimization. In batch cultures, where cells grow without fresh substrate addition, specific rates (per unit cell mass and time) directly yield Yp/s by their ratio, as both normalize to identical cell mass and time units. This simplifies computation without needing absolute concentrations.
Step-by-Step Calculation
Divide the specific product formation rate (qp = 0.215 g/g/h) by the specific substrate utilization rate (qs = 0.25 g/g/h):
Yp/s = qp/qs = 0.215/0.25 = 0.86
This ratio holds because qp and qs share units of g/(g cell·h), canceling cell mass and time to leave g product/g substrate. The result, 0.86, reflects high product yield, common in optimized microbial systems.
Common Misconceptions
Users often confuse Yp/s with Yp/x (product per biomass) or Yx/s (biomass per substrate), but here specific rates dictate direct division. Typical errors include inverting the ratio (yielding 1.2, incorrect) or ignoring units (leading to dimensionally invalid results). True Yp/s excludes maintenance or biomass diversion, focusing solely on product-substrate linkage.
Bioprocess Applications
In biotechnology, Yp/s guides strain selection and media design for antibiotics or biofuels, with values near 1 signaling minimal waste. For this case, 0.86 suggests efficient glucose-to-ethanol conversion in yeast, aiding scale-up predictions.
Correct Answer: 0.86
Perfect for GATE Biotechnology, Bioprocess Engineering exams and academic preparation
