Process for producing calcium citrate from cooked egg shells and membranes

Abstract

The present invention relates to a process for recovering eggshells and their membranes, particularly from the hard-boiled egg processing industry. The process comprises the steps of finely grinding the shells with membranes, converting the calcium carbonate from the shells into calcium citrate by reaction with citric acid under optimized conditions, and then recovering the calcium citrate by centrifugation with water recycling. The calcium citrate obtained has improved bioavailability compared to carbonate and is intended for applications in nutraceuticals, food product enrichment or animal nutrition. This process thus makes it possible to transform a low-value co-product into a high-value-added ingredient, in a circular economy approach.

Description

Title of the invention: Process for producing calcium citrate from cooked egg shells and membranes Field of invention

[0001] The present invention lies in the field of the recovery of calcium-rich co-products. Its subject matter is more particularly a process for recovering eggshells and shell membranes.

[0002] This process is particularly applicable to shells and membranes resulting from the cooking and peeling of hard-boiled eggs. The co-products have undergone heat treatment by cooking. Technological background of the invention

[0003] Consumption of chicken eggs (Gallus gallus) in France is significant, with a national egg production of 15.7 billion in 2021. This high consumption is nevertheless accompanied by a high tonnage of co-products, namely eggshells and their shell membranes. Due to their composition rich in minerals, and more particularly in calcium carbonate, eggshells are now tending to be used for their calcium carbonate, particularly for human or animal food, or as biomaterials, whereas until now they were mainly used as a soil amendment.

[0004] The interest in the recovery of calcium from this co-product is particularly linked to its importance for human health. Indeed, a calcium deficiency can cause a decrease in bone mass and therefore increase the risks of skeletal damage. The daily quantity to be ingested depends on age and sex. For example, for a man aged between 18 and 65, it is recommended to ingest 850 mg of calcium per day, knowing that not all of this calcium will be absorbed during digestion, and this will depend on the bio-accessibility of the form of calcium.

[0005] Calcium carbonate, in order to be correctly assimilated by the body, must be ingested with a meal since this mechanism is notably linked to the presence of vitamin D. The conversion of the calcium form into a more bioaccessible form such as calcium citrate is therefore preferable.

[0006] The aim of the present invention is to determine the optimal operating conditions for maximizing the recovery of eggshells and shell membranes. The objective is to convert them into a product rich in calcium and bio-assimilable by the body. The added value of eggshells is thus improved since this product is intended for nutraceuticals and human food. Summary of the invention

[0007] The present invention relates to an optimized method characterized by the fact that it comprises the following steps which consist of: 1. Grind the cooked, unseparated shells and shell membranes very finely. 2. Convert calcium carbonate to calcium citrate by adding citric acid. 3. Recover a product rich in calcium citrate and recycle the water after centrifuging the product.

[0008] Detailed description of a non-limiting example of the invention

[0009] The process according to the present invention which comprises a chemical reaction is particularly interesting since it makes it possible to recover a large volume of co-products into a raw material with high added value.

[0010] It can be applied to cooked egg shells without membranes or to egg shells not separated from their shell membranes and coming from a hard-boiled egg peeling line. The optimum operating parameters of the reaction were determined by carrying out an experimental design, a central composite design with three factors: temperature, reaction time and reaction volume. Temperature is a very influential factor on the reaction. It is preferable that the process is carried out at room or moderate temperature, with an optimum at 38.5 °C.

[0011] A detailed example of the different steps of the process on eggshells comprising the shell membranes is given below: 1. The first step of the process consists of grinding the shells and shell membranes in a wet process (in a known volume of reaction water corresponding to at least half of the total reaction volume). The objective is to reduce the particle size as much as possible in order to increase the exchange surface between the calcium carbonate and the citric acid. The target particle size is less than 80 μm. 2. The entire reaction volume is added and, with stirring, the mixture is heated to the desired temperature. The reaction can also be carried out at room temperature but will be improved at a moderate temperature of 38.5 °C. 3. Citric acid (anhydrous or monohydrate) is then added under stoichiometric conditions. The acid must be added gradually to avoid excessive foam production. 4. The reaction causes the release of carbon dioxide. Evacuation of the gas is necessary to limit foam production and for operator safety. 5. When all the acid has been added, then the mixture is left under stirring and at temperature for a specific time which varies depending on the chosen temperature. For a moderate temperature of 38.5°C, a reaction time of 2 hours is recommended, and it will be longer for a lower temperature. 6. At the end of the reaction time, a centrifugation process is carried out to recover the product in the pellet. The objective is also to reduce the humidity of the product to 50% to reduce energy costs during drying. The supernatant consisting of water and citric acid is reusable and can be reused for the next reaction. 7. Washing the base with clean water is not necessary but can be done. to improve the purity of the product by removing traces of citric acid in the product. A second centrifugation step will then be necessary. 8. The calcium citrate product is then dried. The drying process produces a product that is stable over time with low water activity (less than 0.5). The final moisture content of the product is less than 10%. 9. Finally, the calcium citrate produced is ground to a desired particle size which will depend on the demands and applications.

[0012] Non-limiting examples of possible uses of the products resulting from the invention

[0013] Possible uses of the product obtained after implementing the method according to the present invention are described below.

[0014] The product contains mainly calcium citrate, and is also composed of calcium carbonate. The protein content is negligible. The product can be used in nutraceuticals as a calcium supplement, and is also intended to enrich calcium products such as fruit drinks or specific prepared meals intended for people with calcium deficiencies.

[0015] The produced calcium citrate can also be used as an ingredient for these functional properties, for example for these emulsifying properties.

[0016] Depending on the volumes produced, the product formed can be intended for animal nutrition, a field for which the use of calcium is significant.

[0017] The product has the particularity of being adaptable in terms of calcium content and its bioavailability. Indeed, if the request concerns a product containing more calcium (lower calcium citrate content), then the reaction can be adapted to meet this need. The addition of citric acid will be adjusted accordingly.

Claims

Claims

1. A process for producing calcium citrate from cooked eggshells, characterized in that it comprises the following steps: a) finely grinding the eggshells with their shell membranes, to a particle size of less than 80 μm; b) mixing the powder obtained with water and heating to a temperature of between 20 and 40°C; c) gradually adding citric acid in a stoichiometric quantity while stirring and discharging the carbon dioxide released; d) maintaining the reaction at temperature for 1 to 4 hours; e) centrifuging the reaction mixture to recover the calcium citrate in the pellet and recycling the acidic aqueous supernatant in a subsequent reaction; f) drying the pellet to a humidity of less than 10%.

2. Method according to claim 1, characterized in that the temperature in step b) is approximately 38.5°C.

3. Process according to claim 1 or 2, characterized in that the reaction time in step d) is approximately 2 hours.

4. Method according to any one of claims 1 to 3, characterized in that it comprises an additional step of washing the pellet with water after step e) and before drying.

5. Process according to any one of claims 1 to 4, characterized in that the citric acid used is in anhydrous or monohydrate form.

6. Calcium citrate obtainable by the process according to any one of claims 1 to 5, characterized in that it has a calcium content greater than 20% by weight and a particle size less than 400 μm.

7. Calcium citrate according to claim 6, characterized in that it has a residual calcium carbonate content of less than 5% by weight.

8. Use of calcium citrate according to claim 6 or 7, as a food supplement, functional ingredient or additive for the calcium fortification of food products.

9. Use according to claim 8, characterized in that the enriched food products are chosen from beverages, prepared meals and animal feed.

10. Use of calcium citrate according to claim 6 or 7, as as an ingredient in cosmetic compositions.