Xoconostle and biotechnology

Currently, many techniques are applied to process the fruits of Opuntia matudæ. Concentrates of xoconostle for Mexican-style food flavoring are not uncommon. Such juices and concentrates are prepared by pasteurizing or sterilizing the juice in thermal equipment.

Xoconostle and biotechnology
Xoconostle. Image: SAGARPA Delegation State of Mexico

Many techniques are currently applied to process the fruits of Opuntia matudæ. It is not uncommon to find xoconostle concentrates for Mexican-style food flavoring. These juices and concentrates are prepared by pasteurizing or sterilizing the juice in thermal equipment that uses fossil fuels such as oil or gas and heats the water in a steam generator boiler that is used to heat the juice in equipment known as a pasteurizer (at approximately 70 degrees Celsius) or a sterilizer (approximately 100 degrees Celsius).

This pasteurization achieves a significant reduction of the live bacteria content and the momentary inactivation of the enzymatic activity in the juice causing the loss of viscosity and loss of color, while sterilization achieves a significant reduction of the spore content and a definitive inactivation of the enzymatic activity in the juice.

It is also common to buy tuna cheeses. There are other products such as powdered xoconostle, which is a bit expensive since it is necessary to heat enormous amounts of air to dry it, with the consequent loss of energy. Perhaps the most famous case was that of the researcher who planned to treat xoconostle with accelerated electrons. Something like gamma rays, but with low energy. It is a way like any other to stabilize the flavor of food. This nuclear pasteurizer has not left the prototype stage, but it has given rise to other processes that may be promising.

The most recent reference is that of Xoconostle juice electro-dialyzed with bipolar membranes. This field of research is all the rage these days. Large industrial groups such as Dupont, Mitsubishi, and Solvay have developed and commercialized synthetic ion-exchange membranes. Electrodialysis with membranes of this type is used in the manufacture of table salt. It has also long been used to produce water (electro-pure or e-pure) and to produce organic acids.

It is possible to perform neutralization reactions using electro-dialysis. This makes it very easy and convenient to adjust the pH of foodstuffs. Electro-dialysis is based on the selective electro-migration of ions through cation and anion exchange membranes. Cation exchange membranes are negatively charged and allow the passage of positively charged cations. Anion exchange membranes are positively charged and allow negatively charged ions to pass through.

In an electrodialysis system, more than 400 to 500 cation and anion exchange membranes are installed in parallel to form an electrodialysis array. Bipolar ion exchange membranes are now available which are the union of a cation exchange membrane with an anion exchange membrane in one. These bipolar membranes are very useful for carrying out water dissociation and can be used to adjust the pH of a fruit juice to the desired level.

Electro-dialysis is a highly energy-efficient process. Its performance depends on the energy dissipated by the system. Compared to traditional thermal processes whose efficiency does not go much beyond 70 %, these systems can reach an energy efficiency of 98 %.

The applications of electro-dialysis to the food industry go beyond water purification. When it comes to marketing unclarified juices there is the problem of browning and the problem of viscosity drop. The non-clarified juice that has been selected to carry out the first experiments is apple juice although protocols for pear juice have also been proposed.

This fresh juice is sensorially unstable because it contains substantial amounts of enzymes and substrates (polyphenols and polyphenol oxidase, causing enzymatic browning; inulin and polyfructosanases causing viscosity drop) but it has been shown in the laboratory that the enzymatic activity of polyphenol oxidase and polyfructosanase can be irreversibly inhibited by a temporary decrease in pH to 2.

Then the pH is returned to its initial value. If this operation on the juice is carried out with acids and chemical bases such as hydrochloric acid or sodium hydroxide, the dilution effect of the addition of acid and base significantly affects the taste of the juice, making it unacceptable. In traditional practice, large quantities of antioxidants such as ascorbic acid or its derivatives were used to prepare these cloudy fruit juices.

This can be avoided by electro-dialysis which lowers the pH by dissociation of water in the bipolar ion exchange membrane inactivating polyphenoloxidase and polyfructosanase. Cloudy apple and many other fruit juices reduce their enzymatic browning if a current density of forty milliamps per square centimeter is applied in an electro-dialysis unit alternating cation exchange membranes and bipolar ion-exchange membranes.

This device acidifies the medium by dissociating the water, which reduces polyphenoloxidase activity by up to eighty percent. It is also possible to restore the initial pH of the juice using electro-dialysis with bipolar membranes. It is sufficient to replace the compartments for the bipolar membrane to neutralize the acidic juice. This procedure can also be used to avoid the viscosity drop and browning of the xoconostle juice.

The method would consist of the following: Xoconostles are washed with cold water and sorted to reject low-quality fruits. Then the fruits are fractionated and the juice is extracted from them. These juices are sieved in a sieve and inhibition operations are started as soon as possible. After acidification in the electro-dialyzer, the juice is transferred to the holding tube (in the same way as in a thermal pasteurizer or sterilizer) where the time necessary for the reduction of enzymatic activity elapses.

The electrodialysis cell for juice acidification consists of two types of cells, a juice compartment, and a conductive medium solution. A bipolar membrane separates the juice and conductive medium solution compartments. The juice circulates on the cation side of the membrane and receives the protons, while the conductive solution on the anion side receives the hydroxyl ions from the dissociation of water molecules. The system is equipped with conventional cation exchange membranes on each side of the bipolar membranes. The specific voltage is around two to four volts.

After treatment, the acidified Xoconostle juices and their controls are stored at holding temperature for the time necessary to achieve the inhibition of enzyme activity that is witnessed by the reduction of microbial and sporulated life. Once the pH of the Xoconostle juice has dropped beyond 2 and the value is retained long enough to deactivate all enzyme activity and microbial growth, an attempt is made to bring the pH back to its initial value.

Source: Vinculando