Microwave browning of vegetables

Details Microwave browning of vegetables Microwave browning of vegetables

1999-11-16

2004-01-27

Cano, Milton I. (Department: 1761)

Food or edible material: processes, compositions, and products

Direct application of electrical or wave energy to food...

Heating by electromagnetic wave

C426S234000, C426S268000, C426S466000, C426S637000

Reexamination Certificate

active

06682764

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods and apparatus which enable vegetables to be browned (e.g. to be provided with a golden brown and/or crisper skin) using microwave irradiation (e.g. in a conventional microwave oven). The invention will be described primarily with reference to its use with root vegetables (in particular potatoes), but it should be appreciated that the invention has broader application.
BACKGROUND ART
Very few attempts have been made to produce microwave-cooked vegetables with comparable skin colours and textures to those produced using a conventional radiant heat oven.
One technique employed to achieve such an effect uses a clear microwavable plastic wrap that is wrapped around the vegetable prior to irradiation. However, this technique does not simulate a comparable colour and crispness of exterior in the skin of such vegetables.
The Maillard reaction has been known to science since the 1940's. The Maillard reaction involves the action of amino acids and proteins on sugars. The reaction results in the formation of melanoidins, which are brown coloured nitrogenous polymers and co-polymers and give the requisite brown colour to food products coated with Maillard reaction components. The Maillard reaction can be activated by microwave irradiation. Various patents in the prior art make use of the Maillard reaction for browning foodstuffs, primarily, flour-containing foodstuffs such as pies, pastries etc, and meat products (see e.g. U.S. Pat. No. 5,089,278, JP08/131092, JP08/308531, U.S. Pat. No. 5,091,200 and GB2228662)
Other types of browning compositions have also been employed in the art, for example, the use of honey, the use of an aqueous syrup comprising a caramelised disaccharide (U.S. Pat. No. 4,252,832), the combination of salts such as potassium acetate, potassium chloride and sodium bicarbonate (U.S. Pat. No. 4,518,618) etc.
U.S. Pat. No. 5,043,173 discloses a browning agent for foodstuffs having a carbonyl-containing browning reactant. Again, this invention makes use of the Maillard reaction but instead of coating a foodstuff with a separate component, use is made of carbonyl functionality within the foodstuff itself. This document discloses that hash brown potatoes can provide the requisite carbonyl functionality, (hash browns being a reconstituted form of potato).
As an alternative to the employment of browning compositions, use has been made in the prior art of microwave “susceptor” materials to achieve browning (i.e. such materials typically being incorporated into containers that surround the food products to be browned). A microwave susceptor material is a microwave-interactive material which converts microwave energy into thermal energy (thereby browning adjacent foodstuffs by convection and radiant heating). Various prior art documents define microwave susceptor materials, including WO91/11893, AU14584/88, AU14998/92, U.S. Pat. No. 4,555,605, U.S. Pat. No. 4,590,349, U.S. Pat. No. 4,594,492, U.S. Pat. No. 4,190,757, U.S. Pat. No. 4,626,641 and U.S. Ser. No. 11377/95. Susceptor materials are typically formed from dielectric materials and can be, for example, an alloy of metals which contains both electrically conductive and magnetic materials.
EP303511 discloses the use of a microwave interactive (susceptor) material for browning dough-type products. It also discloses the use of a Maillard reaction for browning a base of the dough product.
The prior art also discloses various types of microwave shielding materials which are employed in containers and enable an even microwave cooking of foodstuffs located in those containers. Examples of various types of shielding arrangements are shown in EP185488, U.S. Pat. No. 4,345,133, AU47100/89, U.S. Pat. No. 4,233,325, GB2307159, WO92/13432, U.S. Pat. No. 4,626,641 etc.
The microwave browning of vegetables, however, presents special problems. This problem in part stems from the geometry of vegetables, for example root vegetables, wherein these geometries make an even cooking and browning difficult (i.e. The vegetable is not a homogeneous product as is the case with prior art dough-type products etc). Furthermore, for the microwave cooking of whole vegetables the art has actually taught away from the use of a Maillard reaction (i.e. Maillard reactions have been avoided in the microwave cooking of vegetables). This is because a vegetable needs to be, in a sense, overcooked in a microwave oven to achieve cooking therethroughout, and if a Maillard composition were to be present on the exterior of a vegetable, then this would lead to blackening at the high irradiation/cooking rate.
It would be advantageous to provide a technique whereby microwave irradiation, more particularly microwave cooking, of a vegetable simulates the appearance and texture of the vegetable as cooked (e.g. baked) in a conventional radiant heat oven. Such a technique could then take advantage of the fast cooking times and convenience associated with microwave ovens.
SUMMARY OF THE INVENTION
In a first aspect the present invention provides a method for the microwave irradiation of a vegetable to cook the same and to brown the exterior thereof including the steps of:
(i) applying a microwave activated browning agent to the surface of the vegetable;
(ii) prior to irradiation, positioning a shielding means adjacent to the vegetable in a location such that, during irradiation, adjacent portions of the vegetable are shielded from microwave radiation; and
(iii) irradiating the vegetable with microwave radiation to cook and brown the same.
Such a method enables the vegetable to be subjected to controlled microwave cooking, whilst at the same time browning can occur, and microwave intensity can be applied without the risk of an overcooked region developing (i.e. being prevented by the shielding means).
Preferably the browning agent is a Maillard composition. For example, any of the Maillard compositions as defined in the prior art can be employed.
Typically the shielding means is an absorptive and/or reflective material, and in preferred forms in provided in a container housing the vegetable in the form of a strip of material.
Instead of employing Maillard components, other types of browning agents can be used, such as those described above, or colourants dispersed in continuous edible fats or oils (see e.g. U.S. Pat. No. 5,139,800).
The present invention in a second aspect provides a method for the microwave irradiation of an unskinned vegetable to brown the skin thereof including the steps of applying a sugar and an amino acid to the skin and then subjecting the vegetable to microwave radiation for a predetermined period of time.
Thus, an unskinned vegetable (e.g. a whole potato) having, in some way, a sugar and an amino acid located at the exterior thereof, and when irradiated with microwave radiation, can have visual and textural effects imparted to the skin of the vegetable that simulate those that occur using conventional radiant heat. A major part of the browning typically occurs as a result of the sugar reacting with the amino acid, and shielding can be used to achieve both even cooking and even browning.
When the term “vegetable” is used in the present specification, it is primarily a reference to root vegetables such as potatoes, onions, carrots, sweet potatoes, pumpkin, etc, but it should be appreciated that the term is not so limited and may also extend to some types of fruit (e.g. tomatoes).
In addition to the sugar and amino acid, a salt can typically by applied to the vegetable exterior (usually as a mixture with the sugar and amino acid). A typical salt employed is sodium nitrite but sodium chloride, sodium acetate and sodium carbonate are suitable alternatives. More typically the salt is applied as part of the solution applied to the vegetable. The inclusion of a salt with dielectric absorption qualities helps to speed up the browning process. The salt also tends to counteract any sweetness from the sugar and tends to assist in the longer term storage of the so coated vegetable by slowing down m

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