**3. Industrial processing of** *M. integrifolia* **nuts**

In South America and mainly Paraguay, a country with a very hot tropical climate, the rational cultivation of macadamia began in the 1960s, with seedling of genetically improved macadamia species [14]. In the last 10 years, there has been a significant increase in the export volume of this nut (**Figure 2**), ~ 70 tons were exported in 2020, generating important profits to the productive sector.

**Figure 3** shows the main stages of the production process, which begins with the harvest, carried out manually, where the ripe nuts naturally fall off and can be harvested directly from the ground or collected with nets. Harvesting of ripe fruits should be done at least once a week, and this frequency should be increased on rainy days [28]. In the processing plant, the first operation is dehulling, whose purpose is the removal of the green husk (pericarp) that protects the fruit within 24 h after

#### **Figure 2.**

*Evolution of income derived from the export of M. integrifolia nuts in Paraguay. Source: Central Bank of Paraguay.*

#### **Figure 3.**

*Block diagram of the industrial processing of M. integrifolia nuts. Elaboration: Smidt, M.*

harvest. This operation is important because its presence indicates to the seed that it must germinate, which leads to the translocation of sugars in the kernel and the beginning of the formation of a dark halo in the circumference of the macadamia. The carpel is a nutrient-rich material that is usually used as organic fertilizer for the crop itself. The NISs are then subjected to manual cleaning and classification by flotation, which allows the separation of unripe nuts because those with a high oil content sink. This operation also removes foreign particles and allows the product to be washed, but it is only effective when the moisture content of the NIS is greater than 17% [29].

The next operation is the most important phase in the processing of macadamia nuts, drying, which consists of removing water to a level that prevents the growth of fungi and bacteria, in order to allow the preservation of the nutritional quality of the grain as food or its viability as a seed. When the NIS falls from the tree, it has a moisture content of ~25% (wb) in the almond (kernel), which must be reduced to a percentage less than 1.8% (wb) [9], to avoid the attack of fungi mainly, as well as to avoid the oxidative deterioration of lipids.

Studies conducted in Paraguay indicate that moisture can be removed in two stages of drying at low temperature, which prevents kernel rancidity, evidenced by a high peroxide and acidity index. During the first stage, work is carried out at a temperature of 40°C for ~14 h, which allows a decrease from the natural moisture content of the NIS to ~8%, with a minimum air speed of 0.5 m/s. The next stage of drying allows the temperature to be increased to 65°C for ~15 h, a minimum air speed of 5.4 m/s,

#### *Challenges and Advances in the Production of Export-Quality Macadamia and Its Integral Use… DOI: http://dx.doi.org/10.5772/intechopen.105000*

allowing the moisture content to decrease to 1.5%, value required almond packaging. The composition characteristics of macadamia nuts have led to an important assessment of their origin and nutritional and bioactive properties, which has allowed the regulation of the market based on well-established quality criteria. The physicochemical and microbiological quality specifications established and internationally accepted in most markets are moisture content less than 1.8%, peroxides 3–5 mEq/ kg, free fatty acids 0.5% max, total aflatoxins 4–20 ppb, B1 aflatoxin 0–2 ppb, total plate count <30,000 cfu/g, molds and yeasts <20,000 cfu/g, *Escherichia coli* < 3/g, not detectable Salmonella 25 g, coliforms <300 cfu/g, no insect infestation, "normal" uniform cream color, oil-free appearance on surface, no foreign material, and no bad smells or flavors [9].

Laboratory-scale tests were conducted to evaluate the physicochemical and microbiological characteristics of the nuts subjected to drying, which were then transferred to the design and construction of an industrial dryer (**Figure 4**). The heat necessary to dry the nuts was produced by the combustion of the shell, obtained in the next stage of the macadamia processing (cracking); this material is hard and has a high calorific value (~ 19,600 J/g).

The air required for combustion enters through the ashtray, passes through a rack through its slots, and comes into contact with the fuel. The combustion gases circulate inside tubes with an extended surface (fins) to later be evacuated through the chimney. The drying air is driven by a centrifugal fan, circulates transversely to the finned tubes, and is heated by heat transfer from inside the tubes. Finally, the hot air

**Figure 4.** *Silo-type dryer with an air heating system. Source: Adapted from [30].*

enters the silo from the bottom through an inclined rack. A detailed description of the design, construction, and operation of the equipment can be found in [30].

Continuing with the production process, the next operation, once the required moisture content (1.5%, wb) has been reached, is the breaking of the NIS carried out with a breaking machine. The separation of the kernel and the shell is done manually, obtaining a product with variable sizes, with whole nuts (~ 38%) being the most valued product, followed by whole nuts with small cuts (~ 12%). About 31% of the kernels obtained in this operation are halved in the breaking machine and 28% are smaller than half a kernel. Finally, the nuts are packaged to improve their shelf life and prevent spoilage.

Macadamia nuts from South America and other tropical countries have had to face certain challenges in their production and meet these quality criteria such as low levels of moisture and low levels of peroxides. The climatic and soil conditions of tropical countries were appropriate for the implantation of *M. integrifolia* crops and allowed the adaptation of varieties of the exotic species from Australia; however, it has become a nontraditional production item that has gained presence in the national and international market as an exportable resource. The process to reach production levels in South America has been slow and involves a great commitment to offer a product with characteristics that make it competitive in high-demand markets, which are characterized by demanding the satisfaction of rigorous quality criteria, sustainable over time.

The main factors affecting the production of macadamia nuts during postharvest are as follows:


Therefore, the quality of the macadamia nut depends on the conditions of the initial composition of the nuts prior to the drying process and the methods by which *Challenges and Advances in the Production of Export-Quality Macadamia and Its Integral Use… DOI: http://dx.doi.org/10.5772/intechopen.105000*

they are processed, packaged, and stored. To combat these adverse factors for quality, adequate postharvest process, efficient drying systems, and the implementation of packaging systems that reduce susceptibility to lipid hydrolysis and oxidation are proposed in the industry.

Macadamia grain quality is more affected by slow drying at room temperature than by postharvest processes such as the type of huller used [33]. Grain drying consists of the removal of water to a level that prevents the growth of fungi and bacteria, so that the appearance and nutritional quality of the grain as food, or its viability as seed, is preserved [34]. The drying methods for the nuts can be summarized as follows:


<sup>1</sup> Specific flow, which refers to the amount of air received by a cubic meter or ton of grain in a defined unit of time.

drying. Microwave heating works at frequencies between 300 MHz and 300 GHz [37]. Industrial ovens frequently combine both the conventional and microwave heat sources to obtain different degrees of browning and surface crispness, to accelerate moisture removal, and to reduce surface counts of microorganisms. Macadamia nut drying using microwaves, especially from the sensory point of view, allows obtaining a product with characteristics similar to those of the conventionally dried product. The advantage of this process is the lower impact on lipid rancidity, once the drying process is finished and after 6 months of storage [35]. The experiences carried out have been promising in terms of the greater drying speed, but have caused some problems of deterioration of the quality of the kernel, in terms of the characteristic cream color that it should present, without considering that this technology is even more expensive than conventional drying systems [30].

### **4. Macadamia nut packaging systems**

Once dried, the macadamia nuts (kernels) contain a large amount of unsaturated lipids that can still be affected by oxygen, light, humidity, and heat during storage. For this reason, it is necessary that the relative humidity in the storage place does not exceed 70%. Similarly, an excessively dry environment can cause the nut to lose weight and lead to rancidity processes, so it is not convenient for the ambient humidity to be less than 40% [31]. In order to choose the appropriate preservation technique for the storage of dried kernels, it is necessary to know the estimated time and storage conditions of the packaged product.

Packaging fulfills the basic functions of containing and protecting the food, informing and attracting consumers. The use of packaging with new protection techniques has made it possible to extend the shelf life of these foods. The packages used in vacuum systems and protective atmospheres are made with coextruded materials, i.e., those that are made up of more than one polymer, generally low-density polyethylene and polyamides [38].

The appropriate packaging options have proven to be vacuum packaging in modified atmospheres or protective atmosphere.


*Challenges and Advances in the Production of Export-Quality Macadamia and Its Integral Use… DOI: http://dx.doi.org/10.5772/intechopen.105000*

registers a high diffusion through plastic materials; the high solubility of CO2 can lead to the breakage of the package due to the reduction in headspace [39]. Also, CO2 exerts a fungicidal and inhibitory effect on bacterial growth that reproduces rapidly in normal atmosphere. The absorption of CO2 depends on the moisture and fat content of the products; therefore, most foods absorb this gas. In addition, high concentrations of CO2 can cause discoloration and the development of pungent acid flavors [38].

• **Nitrogen (N2):** N2 is a gas that is not very reactive, odorless, tasteless, and colorless. It has a lower density than air, is nonflammable, and has low solubility in water (0.018 g/kg at 100 kPa, at 20°C) and other food components. The solubility of N2 in foods prevents the breakage of packages, if enough gas is included in the atmosphere of the package to balance the reduction in volume due to the passage of CO2 gas to the dissolved form [39]. Nitrogen is fundamentally used in a modified atmosphere to displace and eliminate the maximum amount of oxygen, avoiding oxidation of vitamins, aromas, color, and fats, inhibiting aerobic bacteria [40].

To take advantage of the benefits of the different gases, modified atmosphere packaging usually requires a mixture of at least two gases, with the optimum proportions varying from product to product. An example of commercially available products is the 50:50 gas ratio of N2 and CO2. Packaging in N2, CO2, and mixed N2/CO2 atmospheres can be a useful alternative to control the parameters that threaten the physicochemical and nutritional quality of macadamia nuts. In a practical case study on macadamia nuts produced in Paraguay, the influence of packaging the kernels in different atmospheres for 180 days was studied. The nuts were dried using a silo-type dryer in two stages:

The first consisted of predrying in a silo-type dryer at a temperature of 39°C and 0.932 m3 /min of air input, until reaching a moisture content of 8.0% ± 0.5%. In the second stage, the nuts were processed in a Sherwood 501 dryer from a moisture content of 8.0% ± 0.5% to 1.5% ± 0.3% at a temperature of 65°C and an inlet air flow of 2.00 m3 /min. Maintaining the height of the nuts bed, without exceeding one-third of the dryer capacity.


The dried kernels were packed in polyamide polyethylene bags using a vacuum packing machine up to 8 mbar and then injection of N2, CO2, and gas mixture

#### **Table 1.**

*Centesimal composition of macadamia nuts in postharvest stages, drying and 180 days of storage in different protective atmospheres.*

CO2/N2 (50,50) as a protective atmosphere up to a pressure of 300 mbar. Nuts were also vacuum packed and packed in polyethylene bags as a control for conventional packaging.

Values are presented as mean ± SD (n = 3). In each row, different lowercase letters indicate a statistically significant difference (ANOVA, post Tukey test, *p* < 0.05). Statistical analyses were performed separately at each stage, because the nuts analyzed were not the same in phase.

The results showed that under these drying conditions, the nuts maintain the quality required for export for up to 6 months, conserving the parameters of peroxide index, acidity, mesophilic aerobic count, fungi and yeasts, and coliforms at 45°C. This processing system used allowed to obtain a good quality product, in accordance with national and international standards, at the time of analysis, up to 180 days of storage and kept in a place with low relative humidity. Regarding the organoleptic characters through a sensory profile of taste and texture, there was a significant difference at 45 days; according to the tasters, a lower moisture content was perceived in the nuts packaged in an atmosphere of CO2/N2 (50:50). After 90 days of storage, a greater intensity of the bitter taste was perceived in the nuts packed in a CO2 atmosphere, with a significant difference compared to the samples packed with other gases. At 180 days of storage, a significant difference was observed in the bitter taste of nuts packed under conventional conditions. The most important variation in the centesimal composition of the macadamia nuts was observed between the postharvest stage and the dry raw material; in the postharvest, the nuts presented 18% moisture and it was possible to reach 1% in the drying stage. The results of the centesimal composition of the macadamia nuts obtained in the different stages are shown in **Table 1**.

#### **5. Drying versus browning: color analysis**

Color is a very important quality parameter of macadamia nuts and varies from white to creamy [33]. Variations in ripeness, sugar composition, moisture content, and drying conditions of macadamia nuts contribute to internal browning [41] caused by an accumulation of reducing sugars in the center of the kernel, which, in turn, react with amino acids to give nonenzymatic browning products through Maillard reactions [42]. The roasting process in macadamia nuts is widely used because it improves the shelf life of the nuts, inactivating the oxidative enzyme system (lipoxygenic enzymes) and improves the flavor, aroma, texture, color, and appearance of the nuts through the reaction of Maillard and lipid peroxidation [43]. However, it is the main cause of intense color variations [44]. Conventional industrial roasting (120–160°C for about 10–20 min) must be controlled to achieve the desired color and sensory characteristics. Color variations can be detected by human vision, which is subjective, so detection by instrumental means is better [45]. Currently, color spaces and numerical values are used to create, represent, and visualize colors in a space of two or three dimensions [46]; in the case of food, as agreed by the International d'Eclairage Commission, it is adapted to a system by the CIE 1976 (ISO 11664–4, 2008) where the color space usually used is the L\*a\*b, which is the Euclidean distance between two different colors corresponding to the color difference perceived by the human eye. The L\* value represents lightness and darkness, its value is between zero for complete darkness and 100 for complete lightness, and the parameters a\* (from green to red) and b\* (from blue to yellow) are the two chromatic components, ranging from −120 to 120 [47]. It is necessary to know the color value in each pixel

#### *Challenges and Advances in the Production of Export-Quality Macadamia and Its Integral Use… DOI: http://dx.doi.org/10.5772/intechopen.105000*

of the surface of the macadamia nut in order to perform a detailed characterization of it and thus evaluate its quality with greater precision. However, the colorimeters available in the market measure L\*a\*b in a few square centimeters (~ 2 cm2 ), and therefore, their measurements are not very representative in heterogeneous materials, as is the case of macadamia nuts [48]. On the other hand, the high cost of colorimeters for small producers in tropical countries such as Paraguay has led to the exploration of other methods of color measurement under standard conditions through photographic images. An alternative to measure color is through computer vision techniques [46, 48–51]. With a digital camera, it is possible to record the color of any pixel in the image of the object using three color sensors per pixel. The most widely used color model is the RGB model in which each sensor captures the intensity of light in the red (R), green (G), or blue (B) spectrum, respectively, which can be analyzed and presented in a histogram; these results can later be converted to the L\*a\*b color model [50]. For this conversion, most of the computerized vision systems described in the literature use specialized equipment or algorithms that are not easily accessible to most researchers, a problem that could be overcome with the use of software already available on the market [48].

To solve the problem of color analysis, a simple, practical, and economical method for color measurement was developed, using a BYK byko basic ® light booth (Columbia, USA), illuminated with two 60-cm-long D65 "daylight" fluorescent lamps, GTI Color Matcher ® (USA), a Canon PowerShot SD1400 IS digital color camera, placed horizontally to the samples at a distance of 10 cm and Image J ® and Adobe Photoshop CC 4.0.1.192. software. Color variation was monitored throughout the nut industrialization process. The same parameters were measured on nuts at different conditions; fresh, dried at 65°C (5,36 m/s air flow), in a silo-type dryer (Sherwood model 501, fluid bed dryer), and nuts stored for 180 days vacuum packed in different modified atmospheres (air, vacuum, CO2, N2, and CO2/N2, 50:50; see **Figure 5**). On the other hand, the content of reducing sugars was measured by Clegg's anthrone method, in order to determine the packaging system that underwent the least Maillard reaction during the process from drying to packaging at different atmospheres [52, 53].

Regarding the color of fresh macadamia nuts, a light cream color was observed, with L\* values on the external surface equal to 68.83 ± 1.85. In dry nuts, however, the values obtained for L\* were higher (71.33 ± 1.07), with significant differences being observed (ANOVA and Tukey's a posteriori test, *p* < 0.05), which indicates a greater luminosity in the dry samples (**Figure 6**). Besides, in the internal surface, we

**Figure 5.** *Color of macadamia nuts at different packaging atmospheres.*

#### **Figure 6.**

*External and internal color and content of soluble sugars in dry macadamia nuts, prior to packaging and after 180 days of storage in modified atmospheres. The values are expressed as mean ± SD. The nuts analyzed in each condition are not the same. Same letters indicate that are no statistically significant differences (ANOVA and Tukey's a posteriori test, p < 0.05). \*they express the degrees of statistical significance with respect to dried nuts prior to packaging.*

observed a value of L\* = 72.00 ± 2.92 and in dry nuts 76.75 ± 3.82, observing statistically significant differences, which indicates a greater luminosity in the samples (ANOVA and Tukey's a posteriori test, *p* < 0.05).

After 180-day follow-up of packaged nuts, statistically significant differences were observed in both the external and internal surfaces, and nuts stored with CO2/ N2 were observed to maintain a desirable cream color in external and internal surfaces that was stable for 180 days and good luminosity values (L\*), with respect to the other atmospheres used.

Studies on the influence of modified atmospheres with different gases on the Maillard reaction are limited in the literature; however, Birch et al. [54] evaluated the external color change and the sugar content in macadamia nuts when they were heated for 20 min at 135°C and observed that both L\* value and sugar content decrease as a function of time.

Once the issue of obtaining whole, dry nuts of high sensory and nutritional quality has been resolved, it is imperative to address the waste that this process entails. They are considered the main byproducts of this drying and packaging process; the cracked, broken nuts or powder of the broken and the shell of the NIS. From cracked nuts, one of the best alternatives is to obtain oil, considering a raw material with a high content of lipids, which require rapid processing due to the susceptibility to oxidation. The main alternatives used for the oil extraction with high added value are described below, as well as the use of biowaste such as the oil extraction cake and macadamia nut shells, which are found in frank development at the level of tropical countries in the productive sector of macadamia.
