Biochemical engineering Study Guide

📖 Core Concepts Biochemical Engineering (Bioprocess Engineering) – Engineering discipline that designs/optimizes unit processes using living organisms or biomolecules. Unit Operations – Standard steps (mixing, separation, heat transfer, etc.) adapted for biological systems. Upstream Processing – All steps before product recovery: cell cultivation, media preparation, bioreactor operation, parameter control (temperature, pH, DO). Downstream Processing – Purification and finishing steps: cell removal, filtration, chromatography, formulation. Scale‑up – Translating laboratory‑scale conditions to pilot/industrial scale while preserving product quality, yield, and safety. Key Variables in Bioreactors – Temperature, pH, dissolved oxygen (DO), nutrient feed rate, agitation speed. Biopharmaceuticals – Therapeutic proteins, monoclonal antibodies, vaccines, recombinant proteins (e.g., insulin, erythropoietin). Metabolic / Enzyme Engineering – Modifying organisms or enzymes to improve product yields or create new pathways. --- 📌 Must Remember Biochemical engineer = bridge between lab discovery and commercial manufacturing. Three tiers of food processing: primary (raw → intermediate), secondary (ingredients → food), tertiary (ready‑to‑eat). Golden rice = engineered crop delivering vitamin A – example of nutritional enhancement. Critical bioreactor controls: temperature ± 1 °C, pH ± 0.1 units, DO ≥ 30 % saturation for aerobic cultures. Common bioproducts: biofuels (from algae/biomass), recombinant proteins, viral vectors for gene therapy. Regulatory focus – safety, compliance, cost‑effectiveness are mandatory during scale‑up. --- 🔄 Key Processes Upstream Processing (Cell Culture) Inoculum preparation → Seed train expansion → Production bioreactor. Monitor & adjust temperature, pH, DO, feed composition (batch → fed‑batch → continuous). Bioreactor Operation Set target T, pH, DO. Use PID controllers to maintain setpoints. Sample regularly for cell density, metabolite concentrations, product titer. Downstream Processing Cell removal: centrifugation or microfiltration. Primary recovery: precipitation, ultrafiltration. Purification: chromatography (affinity, ion‑exchange), viral filtration (for gene‑therapy vectors). Formulation: buffer exchange, lyophilization, sterile filling. Scale‑up Strategy Keep geometric similarity (reactor shape) or maintain key dimensionless numbers (e.g., Reynolds, Damköhler). Perform pilot‑scale runs to validate mass/heat transfer and mixing. Bioprocess Optimization Apply Design of Experiments (DoE) → identify optimal temperature, pH, feed rate. Use response surface methodology to locate maximum yield. --- 🔍 Key Comparisons Primary vs. Secondary vs. Tertiary Food Processing Primary: raw → intermediate (e.g., milling grain). Secondary: combine ingredients → finished food (e.g., baking bread). Tertiary: ready‑to‑eat or heat‑and‑serve (e.g., frozen meals). Batch vs. Fed‑Batch vs. Continuous Culture Batch: all nutrients added at start; simple but limited productivity. Fed‑Batch: nutrients added gradually; higher cell density, better control. Continuous: steady‑state operation; constant product output, complex control. Upstream vs. Downstream Processing Upstream: cell growth & product formation. Downstream: product recovery & purification. Bioreactor Types Stirred‑tank: versatile, good mixing, common for microbes. Photobioreactor: light‑dependent, used for algae‑based biofuels. --- ⚠️ Common Misunderstandings “Scale‑up is just bigger equipment.” – Ignoring mixing, oxygen transfer, and heat removal leads to loss of yield. “Higher temperature always speeds growth.” – Most biologics have narrow temperature windows; overheating denatures proteins. “pH control is optional for microbial cultures.” – pH influences enzyme activity and product stability; uncontrolled drift kills cells. “All downstream steps are identical for every product.” – Purification depends on product size, charge, and stability; choice of chromatography must be tailored. --- 🧠 Mental Models / Intuition “Bioprocess = a living factory.” – Think of cells as workers; temperature, pH, nutrients are their working conditions. Keep conditions optimal → higher output. “Dimensionless numbers are the DNA of scale‑up.” – Matching Reynolds (mixing) and Damköhler (reaction) numbers between scales preserves behavior. “Upstream is the “growth” phase; downstream is the “harvest” phase.” – Separate mental checklist for each stage. --- 🚩 Exceptions & Edge Cases Anaerobic fermentations – DO control irrelevant; instead, monitor redox potential and gas composition. Thermophilic organisms – Optimal temperature > 50 °C; standard mesophilic control strategies don’t apply. Photosynthetic bioreactors – Light intensity and photoperiod become critical variables, not just temperature/pH. Highly shear‑sensitive cells (e.g., mammalian) – Aggressive agitation damages cells; use low‑shear impellers or wave‑bioreactors. --- 📍 When to Use Which Choose Stirred‑Tank vs. Photobioreactor → If product is microbial (heterotroph) → Stirred‑tank; if algae‑derived biofuel → Photobioreactor. Batch vs. Fed‑Batch → Early development or small‑scale → Batch; when higher titer needed and feed control feasible → Fed‑Batch. Affinity vs. Ion‑Exchange Chromatography → Product has a known tag (His‑tag, protein A) → Affinity; otherwise rely on charge differences → Ion‑Exchange. Centrifugation vs. Microfiltration for cell removal → High cell density, large volumes → Centrifugation; heat‑sensitive or low‑volume → Microfiltration. --- 👀 Patterns to Recognize Yield drops when pH drifts > 0.2 units – Spot in data tables. Oxygen transfer limitation shows as plateau in dissolved O₂ despite increased agitation. Product degradation often correlates with temperature spikes > 5 °C above setpoint. Viscosity increase during high‑cell‑density cultures → need for lower shear impellers. --- 🗂️ Exam Traps “Higher agitation always improves oxygen transfer.” – May cause cell shear, lowering productivity. “All recombinant proteins are produced in E. coli.” – Many require eukaryotic expression (CHO, yeast) for proper folding/glycosylation. “Downstream processing is cheaper than upstream.” – Purification can dominate cost (up to 80 % for monoclonal antibodies). “Fed‑batch is always better than batch.” – Not true if feed strategy is poorly designed; can cause substrate inhibition. “Scaling by volume alone preserves performance.” – Ignoring mixing and mass‑transfer scaling leads to failures. ---