Spices are aromatic plant substances used primarily for flavoring, coloring, or preserving food. While many uses of spices are interchangeable with herbs, spices are made from seeds, fruits, roots, or the bark portion of a plant while herbs are made from either leaves, flowers, or stems.
Spices are known for their strong flavoring and antimicrobial properties. Since they are often used in small quantities, spices add few calories to food when used normally but can contribute high amounts of vitamins and minerals to the diet when used in larger quantities. Most spices and herbs also have substantial antioxidants, mostly due to phenolic compounds like flavonoids. Antioxidants also act as natural preservatives, which help increase nutritional content in stored food. Before the advent of modern cooling and storage methods for shipped meats, spices were the primary method for preventing spoilage. Spices are available in fresh, whole dried, and pre-ground dried forms. Spices are normally dried and ground for convenience but grinding increases surface area, thus increasing oxidation and evaporation rates. Spice flavor comes mostly from volatile oils that are prone to oxidation and evaporation. Whole spices have a stronger flavor and longer shelf life than ground spices. In general, whole spices have a shelf life of two years, and ground spices have a shelf life of six months. Fresh spices are more flavorful than dried form but are more expensive and have a much shorter shelf life. In addition to food uses, spices have also been used in medicine, religious rituals, cosmetics, and perfume production. The market is large and diversified with one hundred and nine varieties listed by the International Organization for Standardization (ISO). India is the world’s largest producer and exporter of spices, producing about seventy-five of the ISO varieties. Numerous spice blends exist in different parts of the world. Notable spice blends include Masala (India), Curry (India), Berbere (Ethiopia), Jerk (Caribbean), Adobo (Latin America), Mitmita (Africa), Ras El Hanour (Morocco), Chinese Five-Spice Powder (China), Old Bay (United States), and Mixed Spice (England). Trade potential is strong, especially in areas with favorable climatic conditions with significant local demand like Asia-Pacific. A high percentage of spices and herbs, whether traded locally or exported, are produced by small-scale farmers. Factors driving the market growth include increased availability of international cuisine, increased consumer consumption of natural products and convenience foods, and a larger scope of new and attractive taste creations to meet consumer demand. Increased demand and production of spices have created a need for new testing methods for spice analysis, especially for determining spice authenticity and adulteration. One such method that has been examined is NIR spectroscopy.
The history of spices and herbs goes back to ancient times and is almost as old as human civilization. It is believed that early hunters and gatherers wrapped meat in the leaves of bushes, discovering that this enhanced taste. Over time, nuts, seeds, berries, and bark were also shown to enhance the taste as well as masking unpleasant tastes and odors. As early as 3500 BC, ancient Egyptians were using spices for flavoring, cosmetics, and embalming their dead. Spices were used as a food preservative in early times as well. Chinese writings around 2700 BC mention the use of plants for medicinal purposes. Eventually, the use of spices spread from the Middle East and China to the Eastern Mediterranean and Europe. For thousands of years, spices were transported by donkey or camel caravan from China, Indonesia, India, and Ceylon (present-day Sri Lanka) through the Middle East to Europe. Spice trade played a crucial role in history in many civilizations, including Egyptian, Roman, Greek, and Arabian. During the Middle Ages, spices were considered as valuable as gold and gems in Europe and were a driving force in the world economy. Competition and demand for spices among European nations led to the colonization of India and other parts of Asia. Marco Polo mentioned spices frequently in his travel memoirs, which were written around 1300 AD. The demand for spices also led to the Age of Exploration, eventually resulting in the discovery of the New World. Christopher Columbus’ journey in 1492 was a search for a sea route to the land of spices. In 1497, Vasco de Gama was more successful in finding India by sea by sailing around the southern tip of Africa.
Spices have played an essential role in American history as well. Plant-based medicine was the primary source of medicine in the United States from early colonization until about 1930. Even today, many modern medicines are derived from plant-based medicine, such as aspirin from willow tree bark. After the American Revolution, the United States entered the world spice trade without British taxes and trade restriction. American agricultural and manufactured products were traded all over the world for spices. In modern times, the world spice trade has become more decentralized. While spices are no longer as prevalent when used for medicine or as a preservative, the demand for their use for flavoring and their health benefits is stronger than ever.
Spice Processing, Manufacturing, Blending, and Packaging
While there is a large variety of spices and herbs, the general procedure for processing and manufacturing is similar for all types. The first step is to ensure good raw material for harvesting. Premature harvesting of crops will result in a lower quality product. Crops can be harvested early by farmers for fear of theft, urgency for money, or fear of bad weather.
The localized nature of the spice industry can make these things difficult to monitor. Crops must be cleaned and washed before harvesting. Dust and dirt are removed using either a winnowing basket or cleaning machine. After cleaning, crops are washed in potable water before the drying stage. The drying stage for spice and herb crops is crucial for good quality products. If crops are not adequately dried, mold can grow and can reduce the sale price of spices by over 50%. In extreme cases, bacteria can grow on some spices and present a health risk. The drying procedure can differ based on whether the crops are harvested during the dry or wet season. During the dry season, sun drying is adequate for drying crops. This must be done carefully to avoid dust and dirt contamination as well as the threat of rain. Larger farms may use solar dryers to avoid these problems. During the wet season or times of high humidity, dryers using wood are often used. It is important to not overheat or over dry the crops. Specifications for the proper moisture content vary among different spices and herbs but generally vary from 6% to 13%. Some spices require special conditions for drying, such as being dried in the dark to maintain color.
If the spice is to be ground, this occurs after drying. Manual grinders can be used for small scale production. Larger scale production uses grinding mills which must be monitored carefully. Grinding mills create large amounts of dust requiring ventilation and spices can overheat during grinding if the temperature is not kept cool. Ground spices need to be checked for uniformity as well. There are many well-known spice blends and blending occurs after grinding. Ensuring completion of blending and a uniform mixture presents a big challenge for large spice producers. Packaging requirements can vary in different ways, such as different requirements for ground or whole spice, for the type of spice, and need to account for the humidity level. Boxes and sacks are adequate for whole spices if the humidity is not high. Ground spices are typically stored in a barrier film like polypropylene to avoid flavor loss and contamination.
Adulteration, Monitoring, and NIR Spectroscopy
Adulteration is a huge problem in the food industry for both economic and safety reasons. The history of spice adulteration goes back thousands of years and can present different forms. Some adulteration can be defined as incidental, meaning foreign substances can be incorporated into food from negligence or ignorance. This can occur during harvesting. Harvesting at the wrong time can also create adulteration by reducing nutritional value or having a product with an improper moisture level. Farmers may do this out of fear of theft or because they need money quickly. Intentional adulteration occurs with the intent to cause harm or create economic gain. One form of adulteration is mispresenting the geographical origin of a product, which is relatively harmless but still can have economic consequences. A more dangerous and intentional form of adulteration is contaminating spices with other products, both non-toxic and toxic. Examples of non-toxic spice adulteration include tomato skins in paprika, buckwheat and millet in black pepper, and starch in onion powder. Adulteration with toxic substances has led to illnesses and death. One such incident occurred with Hungarian ground paprika which was contaminated with lead oxide, leading to several deaths and dozens of illnesses. Lead oxide can dissolve in hydrochloric acid in the stomach, making it toxic upon ingestion. Another example is Sudan I dye, a known rodent carcinogen and banned food additive, which has been used as an adulterant in both chili powder and paprika. Other dyes that are not approved for use in food have been discovered in ground capsicum. There are inherent challenges to testing for spice adulteration. Methods of contamination by adulteration are constantly evolving and are difficult to assess visually. Current methods for determining spice adulteration are morphological, microscopic, chemical, or DNA based. These tests are usually expensive, time-consuming, and difficult to use on a large scale to determine the authenticity of a spice.
There is a need for fast, non-invasive, and reliable testing methods for spices. In addition to adulteration, moisture and blending tests would be very useful to the spice industry. One potential method that has been examined for spice testing is NIR spectroscopy. Studies have been conducted that use NIR spectroscopy to detect adulterants in spices as well as in other types of food. Many studies have shown excellent results and prove the feasibility of spectroscopic methods as an alternative to traditional testing. Moisture is a well-known measurable constituent using NIR spectroscopy because water is highly absorbing of NIR light. Using NIR spectroscopy as a method to determine drying time should be a feasible application for spices. In the case of blending, determining blending end time presents a difficult challenge. While blending is a proven application in the pharmaceutical industry, blending of pharmaceuticals occurs under controlled conditions and with the same type of ingredients. Building calibrations using natural products can show variability in NIR spectra that are not because of changes in the parameter of interest. In the case of spice blending, differences in raw materials might make it difficult to use NIR spectroscopy as a method. As of this writing, there are no known studies to determine the feasibility of monitoring spice blending using spectroscopic methods. However, large spice companies are interested in finding new methods to determine the endpoint of spice blending. It is likely that studies will be conducted in the future to see if NIR spectroscopy is a feasible method for such measurements.
Process Analytical Technology (PAT) & On-Line Measurements
Process Analytical Technology (PAT) is a framework for innovative process manufacturing and quality assurance. Critical points and parameters during manufacturing of a product are defined and the process is designed in a way that such points and parameters can be measured using analytical tools and instruments for real-time process feedback and control. Such instruments must be able to measure on-line and in a non-invasive manner. Many vendors have developed instruments that are able to measure multiple points in a process with a single instrument, usually using optical fibers and probes. PAT has become an important part of pharmaceutical as well as chemical manufacturing and is beginning to acquire a hold in the food & beverage industry. One such analytical tool with great potential for use in PAT is NIR spectroscopy.
There are significant challenges to implementing PAT in a spice manufacturing environment. NIR spectroscopy has been proven as a useful tool for measuring parameters of interest in the spice industry. Vendors are coming up with new and innovative ways to make on-line measurements a feasible solution for companies. Advances such as improved fiber-optics, in-situ sampling, a transition to integrated automation, improved data management systems, and communication systems in the Internet and Cloud age have all contributed to implementing PAT. The beverage and food industries also present particular challenges due to natural product variability. In the case of pharmaceuticals and chemicals, the manufacturing process is usually conducted in a controlled environment with constituents that rarely show variability in spectral data over time. For foods and particularly agricultural products, there can be marked differences in products due to many factors, such as temperature variability, seasonal variation, differences in soil and nutrients, and different breeds of the same product. Such variability is especially important to account for when performing spice analysis. Such differences can create variability in spectral data that must be incorporated into calibration models when calibrating NIR spectrometers and other analytical PAT tools. This is known as making models “robust” and often requires a larger and more incorporative sample set to achieve the desired results.
Calibration studies have been conducted for monitoring parameters in the spice industry in-line as well as in the laboratory. Results have been good and show that in-line measurements are a feasible tool for spice analysis using PAT. Parameters of interest for quality control of spices include adulteration detection and quantification, moisture, protein, volatile/essential oils and blending endpoint. Full adoption of PAT in the spice industry will require a collaborative effort from process engineers, food scientists, and other contributors to provide the industry with a manufacturing framework for the 21th century.
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