Processing of Tree Nuts

Throughout history, nuts have been considered as the versatile form of food which is still enjoyed as the major source of diet across the world. It is consumed in a variety of ways such as snacks, recipe ingredients, spreads, and as a delicacy. These have emerged as a favorable alternative to unhealthy snacking which helps in maintaining healthy lifestyle. Scientific evidence suggests that consumption of 1.5 ounces (42 g) nuts per day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart diseases.

Introduction: Tree Nuts

Tree Nuts are seeds or fruits consisting of an edible, usually fat – containing kernel and is surrounded by a hard-brittle shell. Botanically, nuts are one seeded indehiscent fruit. These are considered as nutritionally dense food which are a rich source of proteins, vitamin E, vitamin B2, and essential minerals, and fiber. Tree nuts are also high in antioxidants, which is one of the major factors for their rising consumption. Tree nuts contain unsaturated and monounsaturated fatty acids (MUFA) which make them a popular snack for health-conscious consumers. Its superior quality renders them as good substitutes for animal foods. Almonds, hazelnuts, pistachios, and walnuts are some of the most popular varieties of nuts.

Classification of Tree Nuts

From the food point of view nuts may be divided into three main groups:

  • Nuts with High Fat/ Oil Content

This class of nuts are mostly used in the preparation of the desserts as they are rich in oil. Its examples include cashew nuts, walnut, pecan, etc. Majority of the nuts of these group contain, on average, 50% or more of fat.

  • Nuts With High Protein Content:

This class of nuts contains about 20 -25 % protein. Its examples include almonds, pistachios etc. The combined richness in both proteins and fats of this group nuts explains why these are extremely popular and form the basic food in some areas.

  • Nuts with High Carbohydrate Content

Only few nuts are rich in carbohydrates. Chestnuts, for example contains 50 % carbohydrates and is relatively poor in fats and proteins.

Processing of Nuts

Nuts are of a perishable nature and loses its palatability or becomes inedible if not properly processed. Post-Harvesting steps of processing tree nuts include:

  1. Pre-cleaning: Nut cleaning equipment usually combines gravity and air separation by means of screens and fans to separate nuts and foreign objects by their size and density the nuts will first be sifted by a screen with a mesh size equal to the desired nut size. This allows larger debris to be retained on the screen while nuts and smaller objects fall through. Then, the smaller debris can be screened out by running the material from the first step through a second screen with a smaller mesh size. Yet, stems and debris of the same size as the nuts may still be present. One last cleaning step is air blowing, which separates the lighter particles from the heavier nuts.
  2. Hulling & Shelling: During hulling and shelling step, most of the foreign material attached to the nut is removed. There is also an aspiration system that is running parallelly throughout the facility for controlling dust produced during process. The piping runs along the ceiling to suck up as much dust as possible. During initial stage, sets of machines are used for making crack in the hulls and separating them out from the kernels. Nuts are spread out equally among the machines, which have counter-rotating belts to remove the hulls.

3. Separation of Nut Kernels: At the very end of the process, the kernels are taken to the meat deck to further separate out the kernels from everything else, using screens and positive air flow. The hulls and shells are separated and then the kernels are sent to the bucket elevators to be bulk packed into bins.

4. Heat Treatment: Presence of salmonella may be controlled in nuts and nut products by thermal treatment (e.g. oil roasting, dry roasting, steam or hot water treatment followed by drying) or non -thermal treatment (e.g. chemical processing using propylene oxide (not approved for peanuts) or ethylene oxide (for black walnuts only) as well as by implementing a program to prevent post- lethality recontamination prior to packing.

5. Grading and sorting: After the nuts have been sterilized, roasted, shelled and peeled, they must be graded and sorted on the basis of color and size.

6. Packing: The final product is packed into bulk bins or pound bags (where the bags are pulled tight and sewed up on the line) that are palletized and shrink wrapped for shipment.

Despite the food value of nuts, with many people they have a reputation for being indigestible and causing food allergy. These instances occur due to over-indulgence and from poor mastication. Nuts are concentrated foods with little water or roughage. Thus, there is a need for thorough mastication of nuts for proper digestion.

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