Week 2 Flashcards
Quality
Suitability of a product for a specified purpose - judged against defined criteria
Shelf life
Period of time food is considered suitable for sale
Food safety
free of harmful chemical, physical or biological contaminants
Functionality
properties that contribute usefulness for a specific purpose e.g. dough strength
Importance of quality
- Consumer acceptability - sensory properties
- Product consistency for both fresh consumption and processing - Nutrition value
- Reducing waste - meeting specifications
- Trade (price and market share)
How is quality measured?
- Subjective (visual, texture, flavor)
- Objective (texture, color, nutritional, microbiological)
- Quantitative and qualitative measured
- Traditional analytical, instrumental and sensory analysis
- Consumer acceptability
Visual quality attributes:
- The first quality attributes experienced by consumers
- Morphology (size/shape), appearance (color, gloss, clarity, consistency) - Physical defects
- Blemishes
Appearance has a halo effect that modifies subsequent perception of flavor and overall acceptability - visual quality attributes are used for the differentiation of grading for beef
quantitive colour systems
many systems for quantifying colour - RDB, CMYK
CIE Lab* widly adopted for foods - designed to approximate human vision
L* Lightness
aRed-Green
b Blue- Yellow
Texture
Related to the rheological properties of food
- Elastic (solid) can be deformed and will return to shape after distress - Viscous (liquid) resistance to flow
- Plastic (solid) can be molded
Liquids
- Newtonian eg. water, sugar syrup
- Non-newtonian eg. cornstarch+water (shear thickening), tomato sauce (shear
thinning)
Textual quality definition
ISO definition - combination of mechanical, geometrical nd surface attributes perceptible by mechanical, tactile, visual and auditory receptors
Texture is experienced by:
Finger tips: complex ray of mechanoreceptors
- Lips
- Upper surface of tongue: very sensitive to detection of particle size, shape, lubrication
and friction
- Jaw and teeth: sensitive mechanical attributes
Texture analysis in the mouth
Consumers evaluate a lot of things about food texture during a short residence time in the mouth
- Evaluated by hand or in mouth (firmness, springiness, rate of recovery)
- First bite (firmness/ hardness, deformability, factorability, number of particles)
- chew-down (degree ob breakdown, cohesiveness, smoothness, adhesion to teeth and gums, meltability)
- residual after swallowing (number of chews, mouthful after swallow, oral coating
Texture interacts with the way taste chemicals are released from the food matrix
- awareness of texture if often subconscious - when expectations are not met, the reaction may be strongly negative
Instrumental assessment of texture
Texture can be decomposed into measurements of resistance to force - Compression test eg. squeezing
- Shear tests eg. shearing through a food matrix
- cut/break tests eg. applying force to cause a fracture
- Tensile stretch tests eg. pulling a muffin apart
- Theological (viscosity and shear) tests in fluid or semi solid foods
Texture analysis is complementary to physicochemical analysis eg. particle & bulk density
Taste and aroma are combines in flavour perception
- Favour is one of the most important factors in food choice
- The same flavors can be perceived differently by different people - Tastants are released during mastication and delivered to taste
receptors on the tongue and mouth surfaces - Odorants are sensed through the nose but also released form the
food matric to the oral cavity headspace and saliva
5 taste modalities: bitter, sweet, salty, sour, umami
Detected by specific taste receptors on the tongue or in the mouth
- Receptors encoded by different genes
- Variability of expression between individuals
Sweet - sugar, amino acids
Sour - organic acids
Salty - NaCI, K and Mg salts
Bitter - many fundamentally different substances, response involves - 35 different proteins important for recognising poison
Umami - glutamic and aspartic acid, meat broth, MSG
Sensory evaluation
Discrimination testing
- Is product A identical to product B
Preference, acceptance, hedonics testing
- Is product A better than product B? How much do you like it?
Descriptive analysis
- What does the product taste/feel like?
Sensory characteristic - Technique or evaluating characteristic
Hardness
Place sample between molar teeth and bite down evenly, evaluating the force required to compress the food
Sensory characteristic - Technique or evaluating characteristic
Cohesiveness
Place sample between molar; compress and evaluate the amount of force deformation before rupture
Sensory characteristic - Technique or evaluating characteristic
Adhesivness
Place sample on tongue, press it against the palate and evaluated the force required to remove it with the tongue
Sensory characteristic - Technique or evaluating characteristic
factorability
Place sample between molar teeth and bite down evenly until the food crumbles, cracks or shatters, evaluating the force with which the food moved away from the teeth
Sensory characteristic - Technique or evaluating characteristic
Chewiness
place sample in the mouth and masticate at one chew per second at a force equal to that required to penetrate a gum drop in 0.5 seconds, evaluating the number of chews required to reduce the sample to a state ready for swallowing
Factors affecting quality
Genetics (variety)
- Environmental factors
- Soil, nutrients, solar irradiation, rainfall, temperature
- Time to anthesis
- Post harvest management
- Testing methods
Stages of a typical analytics procedure
- Sample
- sample preparation ^Main sources of analytical error
- Measuring
- Data analysis
- Interpretation of the data
Critical aspect/consideration
- Verification of the procedure - comparison with known standard values - Appropriateness of methods
- Cost, practicality
- Does it measure what it is intended ot measure
Types of samples analsyed
- Raw materials
- To determine that a delivery conforms to standards (composition,
contaminants) - To assure consistency of supply
- To evaluate new suppliers
- Finished material to determine that product meets standards and claims
- Process control samples ot monitor operation
- Complain samples
- Competitors samples
Sampling error, sample storage and replication
Common errors from sampling
- Uneven distribution of constituents in foods - Limitations of sampling devices
- Inadequate size of sample
Changed after sampling due to inappropriate storage
- Loss of moisture, microbial spoilage, absorption into containers, loss of volatiles, enzyme reactions, oxidants
Adequate replication
- Technical replicates vs true replicates
Sampling protocols
- Random
- Stratifies
- Systematic
- Judgment
Traditional analytical techniques (destructive sampling)
Spectrometric (spectral properties, calorimetry, NMR)
Chromatographic
Enzymatic (products of biochem reactions)
Immunochemical (ELISA)
Electrophoretic (PAGE, agarose gel electrophoresis)
Gravimetric, volumetric, conductimetric
high-throughput data collection (destructive sampling).
- high throughput methods with reasonable accuracy
- digital technologies for monitoring and recording
- real time, non-invasive
- trade-off between cost, accuracy/ precision, throughput
Near infra-red reflectance (NIR) spectroscopy
- Each type of molecule vibrates in a unique way
- When these vibrations interact with infra-red light they create a unique spectrum
- Deconvoluted signal compared with spectra in a calibration database to identify
quantify molecules in the sample -
Rapid analysis of many foods - Grains, horticultural produce
- Moisture, protein, start, oil fat..
- Non destructive, non invasive, high throughout
- Solid and liquid samples
- Highly portable, on the go
X-ray fluorescence (XRF)
- Handheld XRF analyser disrupts electron in inner shell of atoms - replacement electrons from outer shells emit energy - varies with element
- Elemental signature of product to match that of environment its come from
- To provide consumers assurance of provenance food fraud
