Analysis c2

• Sampling

  Process or act of taking a portion, or sample, that is representative of the whole population
• Population

  Entire lot or the entire production for a certain period of time
• Sample

  A small portion (of the population) taken for analysis
• Laboratory sample

  The sample may be too large to conveniently analyze using a laboratory procedure → only a portion of it is actually analyzed
• Sampling procedure

  1. Sampling

  2. Sample preparation

  3. Laboratory analysis

  4. Data processing

  5. Interpretation
• If the sampling procedure is done correctly, the measurable characteristics obtained for the samples become a very accurate estimation of the population
• The larger the sample size, the more reliable the sampling
• Sample size is limited by time, cost, sampling methods, and the logistics of sampling handling, analysis and data processing
• Replication

  Making repeated analyses by using more than one similar sample
• Replication is NOT the same as making repeated analyses on one similar sample
• Sampling plan

  1. Determine the sample size

  2. Determine the location from which the sample should be selected

  3. Determine the method used to collect the sample

  4. Determine the method used to preserve them prior to analysis
• Factors affecting sampling plan

  • Nature of the population
  • Purpose of the inspection
  • Nature of the method
  • Nature of the product
• Purposes of inspection

  • To estimate the average value of a characteristic
  • To determine if the average value meets the specifications defined in the sampling plan
• Nature of measured property

  • Attributes (does or does not have)
  • Variables (weight, % fat content, % moisture content etc.)
• Nature of population

  • Homogeneous
  • Heterogeneous
  • Finite
  • Infinite
  • Continuous
  • Compartmentalized
• Nature of test procedure

  • Cost
  • Speed
  • Precision
  • Accuracy
  • Destructive vs Non-destructive
• Problems in sampling and sample storage

  • Sampling bias
  • Poor sample storage
  • Mislabelling of samples
  • Legal samples
• Making samples homogeneous

  Grinders, mixers, slices, blenders
• Reducing sample size

  Once the sample has been homogeneous, a small portion is selected for analysis
• Preventing changes in sample

  • Enzymatic inactivation
  • Lipid protection
  • Microbial growth and contamination
  • Physical changes
• Sample identification

  Label carefully and include: sample description, time sample was taken, location sample was taken from, person who took the sample, method used to select the sample
• Soft drinks

  • Carbonated drinks: air bubbles are eliminated by performing the process of making teh tarik / stir
  • Viscous liquids (honey): stir gently with a spatula or glass rod before sampling
• Oils

  • If the oil is crystallized / not clear: heated (~40℃) until dissolved and filtered while still hot
  • If the oil is clear: the sample is stirred slowly several times. Avoid oxidation.
• Grinding

  • Various mills → reducing particle size to achieve sample homogenization
  • Some foods are more easily ground after drying in a desiccator or vacuum oven
  • Grinding wet samples → losses of moisture and chemical changes. Not much problem with frozen samples
  • The grinding process should not heat the sample → avoid overloaded because heat will be produced through friction
  • For heat-sensitive sample, grinders can be cooled with liquid nitrogen and then ground samples are stored at −80 °C
• Cryogenic grinding or cryogrinding

  • Suitable for most materials and ideal for biological samples and materials that are sensitive to oxygen or temperature
  • Performed manually with a mortar and pestle after freezing the sample with liquid nitrogen
  • Or use a specialized grinding equipment with an integrated cooling system that perform the cryogenic freezing and grinding automatically
• Quartering technique

  1. If the particle size or mass of the sample is too large for analysis, it must be reduced in bulk or particle size using quartering technique

  2. The sample is spread on a clean surface and divided into quarters

  3. The two opposite quarters are combined

  4. Now homogenized with negligible differences between each portion

  5. Laboratory (small) portion is taken
• Mesh number

  Number of square screen openings per linear inch of mesh
• The final particles of dried foods should be 20 mesh for moisture, total protein, or mineral determinations
• Particles of 40 mesh size are used for extraction assays such as lipid and carbohydrate estimation
• Sieve method

  • Dry materials of < 50 μm in diameter → passing the sample through a series of vertically stacked sieves with increasing mesh number
  • As the mesh number ↑, the apertures between the mesh are smaller and only finer and finer particles pass through subsequent sieves
  • Sieve sizes have been specified for salt, sugar, wheat flour, cornmeal, semolina, and cocoa
  • The sieve method is inexpensive and fast, but it is not suitable for emulsions or very fine powders
• Enzymatic inactivation methods

  • Heat denaturation
  • Freezer storage (−20 to −30℃)
  • Changing the pH
  • Salting out
  • Adding reducing agents
• Lipid oxidation protection

  • High-fat foods are difficult to grind and may need to be ground while frozen
  • Unsaturated lipids are sensitive to oxidative degradation and should be stored under nitrogen or vacuum
  • Antioxidants may stabilize lipids and may be used if they do not interfere with the analysis
  • Light-initiated photooxidation of unsaturated lipids can be avoided by controlling storage conditions
  • Lipids are more stable when frozen in intact tissues rather than as extracts
• Microbial growth and contamination control

  • Freezing, drying, and chemical preservatives are effective controls and often a combination of these is used
  • The preservation methods used are determined by the probability of contamination, the storage conditions, storage time, and the analysis to be performed