Study Notes
Overview
This study guide covers the essential knowledge for vegetable preparation as required by the OCR J309 specification. Examiners expect candidates to demonstrate a thorough understanding of the functional and chemical properties of vegetables during preparation. This includes the scientific principles of enzymatic browning (oxidation), the impact of preparation techniques on nutritional retention, particularly for water-soluble vitamins B and C, and the physical changes to cell structures that affect texture and sensory profiles. Marks are awarded for precise use of scientific terminology and the ability to link preparation methods to final outcomes. This guide will equip you with the detailed knowledge and practical skills to confidently answer exam questions on this topic.
Key Scientific Principles
Enzymatic Browning
What happens: When a vegetable or fruit is cut, its cell walls are ruptured. This allows an enzyme called polyphenol oxidase to mix with phenolic compounds in the presence of oxygen from the air. This chemical reaction produces brown pigments called melanin, causing the cut surface to turn brown. This process is also known as oxidation.
Why it matters: For the exam, you must explain this process using the correct scientific terms. Credit is given for identifying the enzyme, the substrate (phenolic compounds), and the role of oxygen. Understanding this allows you to explain how to prevent it, which is a common application question.
Specific Knowledge: The enzyme is polyphenol oxidase (PPO). The browning is a result of melanin formation. Prevention methods include acidulation, blanching, and exclusion of oxygen.
Nutrient Retention
What happens: Vegetables are a key source of vitamins, but some are lost during preparation. Water-soluble vitamins, specifically Vitamin C (Ascorbic Acid) and B-group vitamins, are the most vulnerable. They can be lost through leaching (dissolving in water), oxidation (exposure to air), and enzymatic degradation.
Why it matters: Examiners frequently ask how to maximise nutrient retention. You need to identify the at-risk vitamins and explain the mechanisms of loss and prevention. Marks are awarded for justifying preparation choices based on nutritional outcomes.
Specific Knowledge: Know the difference between water-soluble (B, C) and fat-soluble (A, D, E, K) vitamins. Be able to explain leaching, oxidation, and strategies like minimal water use, preparing just before use, and using acidic mediums.
Professional Preparation Techniques
Knife Skills & Safety
What it is: Using standard, precise knife cuts not only ensures even cooking but also demonstrates a high level of skill (AO3). Key cuts include julienne, brunoise, chiffonade, macedoine, and paysanne. Safety is paramount, and you must know the bridge hold and claw grip.
Why it matters: Vague descriptions like 'chopping small' will not earn marks. You must use the correct terminology and, where possible, the standard dimensions for each cut. This demonstrates technical proficiency.
Specific Knowledge: Be able to name and describe at least four different classical knife cuts and the two main safety grips.
