This document discusses microbial secondary metabolites and methods for strain improvement. It also discusses various types of food additives, including their purposes and common examples. Food additives can be used to improve storage properties, increase healthfulness, make food more appealing through colors, flavors and sweeteners, and improve processing and preparation by acting as stabilizers, antioxidants and more. However, some additives like nitrites have raised health concerns.

1. Microbial secondary metabolites and strain improvement
• SMs- compounds with varied and sophisticated chemical
structure
• By microorganisms and some plants
• Biosynthesis families
- Metabolites derived from shikimic acid eg. Ergot
alkaloids
- Metabolites derived from aminoacids eg. β-lactam
antibiotics
- metabolites derived from acetyl coA eg. Polyketides and
terpenes
- Metabolites derived from sugars eg streptomycin and
kanamycin

2. Strain improvement- classical genetic method
 Mutation followed by random screening
 Careful fermentation tests are performed and new improved
mutants are selected
 Rational selection- selection is made for a particular
characteristics of the desired genotype
 Requires some basic understanding of the product metabolism
and pathway regulation

3. Strain improvement- molecular genetic methods
 Targeted duplication or amplification of SM producing gene
- can be targeted gene duplication and whole pathway
amplification
 Inactivation of competing pathways
-by transposon mutagenesis, gene disruption or inserting an
antisense synthetic gene
 Secretion mechanisms
several protein hyperproducing yeast strains have been
constructed by increasing specific genes of the secretion
path
 Expression of heterologous enzyme activities
incorporate a new enzymatic activity in the strain

4. What is a Food Additive
 Food Additive = any substance a food producer intentionally
adds to a food for a specific purpose
 Direct food additives are those that are added to a food for a
specific purpose in that food. For example, xanthan gum used
in salad dressings, chocolate milk, bakery fillings, puddings and
other foods to add texture is a direct additive.
 Indirect food additives are those that become part of the food
in trace amounts due to its packaging, storage or other
handling.

5. Common Food Additives
 Acesulfame – K (Artificial sweetener, used in chewing gum)
 Aspartame – Artificial sweetener
 Azodicarbonamide – Bleaching agent in flour
 Guar Gum – Stabilizer for ice cream and soups
 Saccarin – Artificial sweetener
 Sodium citrate – pH controller; meat curer
 Sorbitol – Nutritive sweetener
 Tartaric Acid – pH controller used in soft drinks

6.  The purpose of additives fall into four categories
1. Improve storage properties
2. Increase healthfulness
3. Make food more appealing
4. Improve processing and preparation

7. Improving Storage Properties
 Preservatives are added to prolong the shelf life of foods
by preventing or inhibiting microbial growth.
 Benzoic acid and sodium benzoate have been used for
many years as antimicrobial agents in foods.
 They have been used widely in carbonated drinks and fruit
juices.
 Sodium benzoate is considered to be most active against
yeasts and bacteria.

8. Increasing Healthfulness
 Increasing additives is also included in boosting a food’s
nutritional profile.
 Fortification = is adding nutrients that are not normally found in
a food (eg. Milk is fortified with vit. D)
 Restoration = nutrients that are lost in processing are returned
to the food with the process called restoration (reestablishes the
product’s original nutritive value eg. Vit. C is put back into
canned oranges)
 Enrichment = adding nutrients lost in processing (contain more
nutrients than existed in the food before processing (eg. Vitamins
are increased)

9. Making Food More Appealing through color
 Food colorings are added to enhance the visual appeal of food
products. Colors may be derived from natural compounds,
such as chlorophyll and carotene, or they may be synthetic
such as, allura red. Among the natural coloring agents, the
carotenoids is the most widespread.
 The artificial dyes are purified synthetic compounds whose
toxicology has been studied in detail, whereas the natural dyes
are often complex mixtures whose only toxicologic assessment
is that humans have used them with apparent safety for many
years.

10. Making Food More Appealing through flavor
 Sensory additives are compounds used to change or
maintain aroma, flavor (e.g. synthetic esters, aldehydes,
and ketones or plant extracts, and essential oils), texture,
or the color of foods.
 More than 2000 natural and synthetic flavors are available.
 Flavor enhancers are substance that gives no flavor but bring out
the flavor in the food.
 Flavor additives constitute the largest group of additives used in
foods, about half are natural, and the remainder is synthetic.
Frequently used natural flavorings are derived from spices and
fruits (clove, ginger, lemon, pepper, vanilla).

11. Making Food More Appealing - sweetener
 Sweeteners are basically either nutritive or nonnutritive
 Nutritive sweeteners metabolize to produce calories
 Examples are sugar (sucrose), brown sugar, maple
syrup, molasses, and honey.
 Non-nutritive sweeteners - The need for low-calorie or
nonnutritive sweeteners has been recognized for the
control of diabetes and for others wishing to restrict sugar
intake.
 Saccharin, aspartame, and other sweeteners have been
introduced by the soft-drink industry, with one of the most
successful being sodium cyclamate; because it did not leave
the bitter aftertaste characteristic of saccharin.

12. Improving Processing and Preparation
 Stabilizer, substance that keeps a compound, mixture, or
solution from changing its form or chemical nature.
 Example without stabilizer, the fat in peanut butter separates
from the protein, creating an oil pool over a stiff paste.
 Ice cream is creamy, in part because thickeners
prevent crystals from forming as it freezes and
stabilizes.
 Many stabilizers are natural and starch-based.
 Some are made from pectin, casein, sodium
caseinate, and gelatin

13. Antioxidants
 Lipids in foods can undergo oxidative degradation that results in
off-flavors and off-odors.
 The use of food antioxidants is effective in preventing or
retarding certain oxidation reactions, such as lipid oxidation of
unsaturated fatty acids, which produces a "rancid" flavor.
 Some antioxidants are also added to fruits and vegetables to
prevent enzymatic browning.
 Most of the naturally occurring antioxidants, as well as the
synthetic antioxidants used in foods, are phenols.

14. Concerns About Food Additives
 Some people believe that some additives cause “more
trouble than they’re worth.”
 Example – nitrites react with amines (preservative in meat)-
suspected of causing cancer