LESSON 8 PRINCIPLES OF REFRIGERATED
GAS STORAGE OF FOODS
There are clear benefits from the cool temperature storage of foods. As this.
thesis evolved there was another development which paralleled it. While slow.
in maturing, it also had significant potential. The area dealt with the gas,
storage of flesh foods. The matter had appeared in quite an unexpected system─refrigerated dough. In this lesson we will explore the nature and direction. of
the technology of gas storage as it is evolving.
Gas Packed Refrigerated Dough
Cooking is the art of preparing foods by heating until they have changed in
flavor, appearance, tenderness and chemical composition. Baking is a form of
cooking that is carried out in an oven. Baked bread is not only one of the most
ancient foods manufactured by man, it is also the food most widely eaten in the
world. The actual baking process is really the last and most important step in
the production of bakery products. Through the agency of heat, an unpalatable
dough mass is transformed into a light, porous, easily digestible add appetizing
product.
Freshly baked products can be produced and distributed effectively However,
the storage life of soft baked goods is generally less than a week. During
this time, products stale and lost! desirable tastes and textures. The appealing
aroma of baked goods is slowly lost after the products are removed from the
ovens. For best eating, baked products are generally soon after baking.
An ingenious means of providing consumers with ready-td-bake dough products evolved in the past few decades. This product line is called refrigerated
dough. The essential technology involves the preparation of a dough, packaging
it in a sealed container capab1e of holding about 5 atm of gas, and causing an
initial controlled release of carbon dioxide. Under refrigerated conditions, slightly above freezing, such products can be effectively produced and distributed,
and when baked yield excellent products.
Matz(1968) reported that in such commercial refrigerated dough practices.
there is ordinarily used, as the leavening agent or gas generating component a slowly rating sodium acid pyrophosphate ot the approximate formula Na2H2P2O7 in combination with sodium bicarbonate. All ingredients are mixed under very rigidly controlled temperature conditions. (Note: dough temperature out of mixer, 10℃ to 15℃) The resulting dough is rolled out and the dough is then sheeted and cut into banks, such as discs about 5 cm in diameter by l.2 cm thick. The cut-outs are dusted with rice flour or oiled to prevent sticking together. They are then stacked and packed in a suitable can. These cans are doughtight but not gas-tight. As a result, air and carbon dioxide may and do escape so that the dough reaches and blocks the gas outlets. Within about l.5 to 3 hr after the package is sealed, for instance, the biscuits will have so expanded as to fill the container and close the original vents for gas and the internal pressure of carbon dioxide gene ated by the leavening materials will have risen to around 1 atm. Pressure within the can will be maintained over a period of 8 weeks or so if the biscuit dough and cans are normal and the storage temperature is between 7℃ to 12℃.
One of the difficulties in the manufacture of dough using phosphate leavening agents has been the formation of visible phosphate crystals (disodium phosphate dodecahydrate). This crystal formation occurs at storage temperatures below 10℃, and is frequently most abundant at about 7℃. This crystallization is prevalent in the canned refrigerated doughs because of their extended storage, including and normal period of transportation and storage in the stores and homes. These visible crystals cause consumer rejection of the product because of their glass-like appearance and an uneven coloration of the baked goods which develops upon baking.
It is found that phosphate leavened cereal doughs can be prepared. which
can be kept at their normal storage temperature (i.e., between about 7℃ and
12℃) for periods up to 12 weeks or more, and which are free from visible phosphate crystal formation. Such a dough is made in the conventional manner, by
mixing the ingredients such as flour, shortening, flavoring, water, the usual
minor ingredients, and the chemical leavening agent, and then allowing the dough
to develop, and shaping the dough as desired.
The dough is then Placed in the consumer container and sealed, then allowed to proof rapidly so that dough temperature teaches 14℃ to 20℃ as quickly
as possible. Proofing involves the reaction of the chemical leaveners to provide
sufficient carbon dioxide to cause the dough to expand and fill the container so
as to close the gas vents.
The canned dough is cooled in a conditioning area, such as controlled temperature room, at a temperature above its freezing point but below O℃. Normally the freezing point of such doughs is about -6℃. The time and temperature required to condition the dough will vary dependent upon can dimensions, net weight of the dough, formation of the dough, and refrigeration conditions used. However, it is important that the temperature of the conditioning room not be below the freezing point of the dough. The necessary time and temperature can be determined by withdrawing sample cans at intervals. opening them, and noting the temperature and condition of the dough. When microscopic crystals of disodium phosphate phosphate dodecahydrate are observed dispersed substantially uniformly throughout the dough, the dough is conditioned and will not exhibit visible phosphate crystals even after 12 weeks of storage. Once the time has been obtained for a given product under given cooling conditions, the same time of treatment can be used for subsequent production.
Conventional refigerated doughs can be conditioned by being held at about
-7℃ to -5℃ for about 48 hr. With a higher temperature it is recommended that the bolding time be increased to 4 days. At temperatures of about -1℃ a longer holding time of about 3 days is required to obtain proper conditioning of the dough.
After the canned dough has been conditioned, the cans are removed from
the cooling area and transferred to the usual storage area where the temperature
is maintained at 4 to 10℃. The cans may then be transported and the dough
used in the ordinary manner.
Gas Storage of Fruits And Vegetables
Controlled atmosphere (CA) storage
Controlled atmosphere (CA) storage refers to the composition of the atmosphere altered from that of air in respect to the proportions of O2 and/or CO2. The proportioas are controlled; O2 usually is lower and CO2 [increased; nitrogen acts as an inert “filler,” other gases may be added in low concentrations.
Modified atmosphere (MA) storage is similar in principle to CA storage. except control of gas concentrations is less precise. Respiratory CO2 or CO2 derived from dry ice accumulates and Oz decreases.
Lipton (1975) believes that the modification of the O2 and/or CO2 concentration in the atmosphere surrounding fresh produce is justified if the vegetable or fruit will be more valuable after CA storage than after a similar storage period in the air. CA is used most commonly to slow ripening of fruits, but appropriate mixtures of O2 and CO2 also can retard the spread of certain diseases and lower the incidence of some disorders. This is usually not apparent when storage time is brief and/or when storage temperature is optimal.
The use of CA can also prevent desirable ripening. induce severe physiological disorders and cause an increases in decay when misused. Each kind of vegetable and fruit has its own specific, unpredictable tolerance for atmosphere modification .
Controlled atmosphere storage bas been commonly used to delay ripening of fruits, retard the spread of disease, lower the incidence of storage disorders and inhibit toughening and yellowing. An extension of this technique is the use of packaging films to develop a microcontrolled environment in retail packages. Modification of the storage environment by suitable packaging can provide storage benefits which exceed those observed with refrigeration and controlled atmosphere.
Produce Package System
A package of apples can be a dynamic s)-stem in which two processes, respiration and permeation, occur simultaneously. There is an uptake of O2 by the apples and evolution of CO2, C2H4, H20 and other volatiles, and, at the same time. specific restricted exchange of these gases through the packaging film. Variables that affect respiration are: weight of apples, stage of maturity, membrane permeability, temperature, 02 and CO2 partial pressures, ethylene concentration, light, etc. Variables affecting gas exchanges into and out of the package are; structure of the packaging film, thickness, area, temperature, O2, and CO2 concentrations .
It has been demonstrated that steady state conditions are established within
suck an intact packaging system; equilibrium concentrations of 02 and CO2 prevail, and the respiration rate is equal to the rate of gas exchange. Any change in the system variables will affect the equilibrium or the time to establish steady state conditions. The packaging of fresh food in polymeric films is now frequently used in retail stores and about 40% of the produce is now distributed to retail stores in consumer packages. This packaging is designed for consumer appeal. Better use to regulate ripening and, thus, to prolong useful storage life is predicted by many people.