Practical Guide to Vegetable Oil Processing

Monoj Gupta

• Publisher: Academic Press and AOCS Press
• Year: 2017
• ISBN:
  9781630670511
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Practical Guide to Vegetable Oil Processing, Second Edition, includes an up-to-date summary of the basic principles of edible oil refining, processing, and deodorizing, serving as a hands-on training manual for chemists, engineers, and managers new to the industry.

The 15-chapter book includes current information on the bleaching of green oils and coconut oil, quality requirements for frying oil applications, and more. Written for the non-chemist new to the industry, the book makes it simple to apply these important concepts for the edible oil industry.

• Provides insights to the challenges of bleaching very green oils
• Includes new deodorizer designs and performance measures
• Offers insights on frying oil quality management
• Simple and easy-to-read language

Chapter 1

Requirement for Successful Production and Delivery of the Refined Vegetable Oils

Abstract

Crude vegetable oils require refining before they are consumed. The refining process removes as well as reduces the impurities present in the crude oil. Vegetable oil refining technology offers sophisticated equipment. However, the sophisticated equipment is not capable of producing high quality refined oil unless the starting crude oil is of good quality. Various factors can affect the crude oil quality and have been discussed in this chapter.

Keywords

vegetable oils

vegetable oil processing

vegetable oil refining

trans fatty acids

shortening

Vegetable oils are refined with care so the resulting oils as well as the products formulated with the oils are of high quality.

In the rest of the book the various processing steps, their operating conditions, corrective actions through troubleshooting, etc. have been discussed for the reader. All of the processing conditions described are to assist the oil processors to understand the principles of oil processing and produce the best quality refined oil at the plant.

It must be stressed that even after using the guidelines provided in this book, one may not be able to produce the best quality refined oil if the incoming crude oil is not of high quality. It may sound strange, but the success of obtaining the highest quality finished oil depends greatly on the quality of the crude oil received at the refinery.

1.1. Crude oil

Crude oil quality can vary and it depends on various factors that are not directly under the control of the oil refiner. Poor quality crude oil creates certain difficulties in the refining process along with the oil quality issues. Several tips to procure the highest quality crude oil are discussed in this chapter so the refiner is aware of these factors and can take certain actions in the refinery to minimize the negative impact of some of these factors.

1.2. Oilseeds

As mentioned earlier, good quality of the refined oil starts with the high quality oilseeds or oil-bearing fruits and nuts. The quality of the crude oil depends on various factors, such as:

• maturity of the oilseeds,

• harvest conditions (excessive rain or drought condition before harvest),

• handling of seeds,

• seed storage conditions, and

• insect infestation of the seeds.

(In the subsequent discussions only oilseeds will be mentioned. Fruit palm and oil-bearing nuts will be discussed separately.)

1.2.1. Maturity

Immature soybean seeds can exhibit various deficiencies. The crude oil may exhibit some different fatty acid profile and also some variations in the other components in the seeds. This may slightly impact the processing conditions and performance of the refined oil in certain applications. There are numerous literature references that indicate the following:

• The immature seeds tend to have lower lipoxygenase activity, trypsin inhibitor, and urease activity compared to the mature seeds.

• The immature seeds tend to have higher contents of FFA (free fatty acids) and chlorophylls compared to the mature seeds.

• Oil content and total protein contents are not very different between the immature and mature seeds.

• There are minor differences in some individual protein contents between the immature and mature seeds.

Therefore, the oil refiner may receive crude soybean oil that contains high chlorophyll because of immature soybeans. This will require some additional degumming and bleaching steps. This will be discussed in the chapter on bleaching.

1.2.2. Harvest Condition

1.2.2.1. Wet Harvest Condition

Soybean, sunflower, cottonseed, and canola crude oils can exhibit higher than normal green color when the seeds are harvested before they reach maturity or the harvesting season is too wet. The crude oils will require extra steps to remove the excess chlorophylls from them in the degumming and bleaching steps. The refined oil may have lower stability if these steps are not followed properly.

1.2.2.2. Dry Harvest Condition

Dry harvest condition due to droughts can cause physical damage to the seeds resulting in higher than normal FFA and oxidation in the crude oil. The oil will exhibit lower than normal stability.

1.2.3. Handling of Seeds

The seeds, if damaged, during harvest and transport and storage, the crude oil can develop higher FFA and exhibit higher oxidation. This oil will require extra steps in the refining process and will typically exhibit lower stability than normal.

The seeds are dried to <10% moisture before storage. The drying condition requires controlled air temperature and flow around the seeds during the drying step. The seeds may develop case hardening if the air temperature is higher and or the airflow rate is higher than normal. This can develop surface cracks in subsequent handling of the seeds and the crude oil will exhibit higher than normal FFA and initial oxidation.

1.2.4. Seed Storage

It is important that the seeds are properly dried to <10% moisture and stored under 40°C (104°F) with proper air ventilation. At temperature of 45°C (114°F) or moisture content of 14% or higher, the oilseeds develop higher concentration of nonhydratable phospholipids. This makes degumming, refining, and bleaching processes more difficult and it also results in higher refining loss and also the refined oil quality is compromised. In addition, there is color fixation of the oil. The crude oil develops darker than normal color that cannot be reduced through the normal bleaching process. The crude oil in most cases has to be treated with stronger alkali solution to reduce the color.

1.2.5. Insect Infestation

Typically, dry growing season and drought condition tend to promote insect damage of the seeds. This results in higher than normal FFA and initial oxidation in the crude oil. As described in some of the previous conditions, the crude oil exhibits higher than normal refining loss and lower stability of the oil.

1.3. Additional comments on oilseeds

Oilseeds mature at a slight different rate between the top and lower parts of the plant. This tends to be more pronounced in case of cottonseed. Similarly the soybean pods can have different degree of maturity on the same plant and not all the seeds on the same sunflower would be identical in maturity. Therefore, a lot of oilseeds shipment may contain some seeds that are somewhat less mature.

The oilseeds in a lot will always have some damaged (broken) seeds, some with lesser degree of maturity. However, the various grades of seeds that are sold under USDA specification seem to perform in a uniform manner in producing the crude oil of desired quality.

Higher than normal level of diglycerides are formed whenever the crude oil is treated with stronger than the normal strength of alkali solution used in the process. Sometimes the crude oil is alkali treated more than once to meet the refined oil specification on FFA and/or color. The excess alkali or stronger alkali can attack the neutral triglyceride molecules in the oil (in addition to the FFA), forming diglycerides. Diglycerides are emulsifiers. High concentration of diglycerides in the alkali treated oil makes it difficult to separate the aqueous phase from the oil phase in the soap separation stage. This tends to increase the loss of neutral oil in the soap causing higher oil loss in the refining process.

1.4. Fruit palm

The fruit palm is harvested from the tree when they reach maturity. Like in case of oilseeds, the fruit palm on the same bunch may have somewhat different degree of maturity. Usually, the very ripe ones get damaged or ruptured under the normal harvesting procedure.

Lipase and lipoxygenase activity begin in the oil inside the fruit palm when the skin of the fruit is damaged. The fruit is treated for enzyme deactivation and the oil is extracted as soon as possible after the harvest. However, most commercial crude palm oil (CPO) contains as much as 5% FFA and the diglycerides content is typically 5%.

Whenever a molecule of FFA is formed from hydrolysis of a neutral triglyceride molecule, a diglyceride molecule is formed. When the palm fruit is damaged during harvest, the enzyme lipase hydrolyzes the triglyceride molecule forming FFA and diglyceride.

The author studied the damaged fruit palm and the impact on the FFA of the oil in a palm plantation in Costa Rica. Following tests were performed:

1. The damaged fruits from a fruit bunch were collected and weighed.

2. The total weight of the fruit palm in the bunch was taken.

3. It was found that the ruptured and damaged fruit constituted 6% of the total weight of the fruit in the bunch.

4. FFA content in the oil extracted from the damaged fruit was found to be 50%.

5. Therefore, it was estimated that whatever the FFA of the oil from the fruit palm extracted from the whole bunch would be increased by 3% (0.06 × 50 = 3.0).

6. Thus, the majority of the FFA in CPO would have come from the over ripe and damaged fruit.

Typical commercial production of CPO does not separate the damaged fruit from the rest for oil extraction.

There are companies, such as Sime Darby Jomalina that do separate the damaged fruit before extraction in order to produce low FFA and low diglyceride CPO and refined PO and palmolein. Sime Darby Jomalina can deliver palm oil and palm oil fractions with guaranteed quality (JGQ). There are other companies in Malaysia that are also capable of delivering low FFA and low diglyceride palm oil if a customer needs it.

High diglyceride content in the palm oil increases the FFA in a fryer faster and also slows down the rate of crystal formation in the shortening and margarine process.

1.5. Groundnuts (peanuts) and tree nuts

The same comments made in connection with the oilseeds also apply for these oil-bearing nuts. An important additional issue that can be experienced with nuts is mold that can produce aflatoxins. Aflatoxin is a type of mycoto...