Quality control (QC) is an essential part of any manufacturing. Without it there's no way of knowing whether the product leaving the factory is up to scratch. For manufacturers of discrete products and components - such as cars, computers, mobile phones and the other paraphernalia of modern life - this is a straightforward operation. If a component or product fails QC, it's rejected and the production line carries on.
For food manufacturers, however, it's seldom an individual product that gets rejected when the QC lab comes up with bad news - it often has to be the entire batch if changes to the process can't be made fast enough. This is why food processors are constantly striving to speed up the time between taking samples off the production line and getting the results back from the laboratory. But what if samples didn't have to be taken away from the production line in the first place? What if the laboratory is taken to the process instead?
This is the thinking behind new developments in on-line and at-line techniques now coming out of universities and into the mainstream of analytical technologies.
On-line (or in-line) measurements in this context are generally taken on the bulk material flowing through the process - whether in pipes, on conveyors, or in mixing vessels.
At-line measurements, on the other hand, are performed on samples taken from the process as with lab testing, but using analytical equipment immediately adjacent to the process lines. In both cases the result is the same - speeding up the feedback time from results to action.
Food Sensors Network
The Food Sensors Network, for example, was set up in 2003 with funding from the Department for Environment, Food and Rural Affairs (DEFRA) and industrial members of the network with the aim of exploiting and developing some of the latest sensor technologies in these areas. Typical of the network's projects is that of Dr Pradip Patel, who heads up the team at Leatherhead Food International, which runs the network.
In collaboration with the University of Luton and companies such as Omron Electronics, Sira, Nutriblend, Nestlé and Kellogg, he is researching an in-line sensor for measuring micronutrients (primarily vitamins A and B2) in flowing food systems. He says this is a major problem for companies manufacturing nutritionally fortified foods or foods such as slimming aids that need to be able to monitor and control the level of micronutrients in order to address issues such as label claims, and quality and safety of the products.
At the European level, the European Union (EU)-funded GoodFood research project is looking to develop a new breed of biosensors for use in on- and at-line equipment. According to Carles Cané, the coordinator of the project at Spain's National Microelectronics Centre in Bellaterra: "In order to bring the lab to the food, rather than the food to the lab, we are employing tiny biomechanical and microelectronic sensors of the kind already being used in the medical field to detect diseases. The real innovation is the way in which we are applying nano- and micro-technology." The first fruits of the research are being tested during the course of this year at a vineyard near Florence in Italy, where the grapes due for harvesting in September will have been grown under the watchful eye of the biosensors.
Meanwhile, demonstrating the global interest in on-line technologies, US analytical equipment manufacturer Thermo Electron Corporation has recently teamed up with its local university in Minneapolis, Minnesota. The group is working on a two-year project to investigate laboratory-based techniques and technologies that are currently used to analyse food by periodic sampling. They will then determine how these systems can be developed into on-line process instruments.
"There is considerable interest in process analytical technology for the pharmaceutical industry," says Dr Ted Labuza of the University of Minnesota's Department of Food Science and Nutrition. "But this is a pioneering effort for the food industry. Food characteristics that could be measured include quality aspects such as moisture, colour and fat, or the presence of contaminants such as aflatoxin."
Fluorescence spectroscopy
Focusing on the technique of fluorescence spectroscopy, the Minnesota project is one of several under way at Thermo Electron to bring new process analytical techniques to market. But the company has already made considerable inroads into the on-line and at-line markets with its near infrared (NIR), Fourier Transform infrared (FTIR) and Fourier Transform near infrared (FT-NIR) spectroscopy technologies.
Introduced at the end of last year, for example, the company's Nicolet Antaris FT-NIR analyser can analyse fat and dry matter in cheese in seconds while it is being processed ? offering a distinct advantage over the conventional lab-based methods. Traditional cheese analyses generally require a skilled operator running multiple samples in order to get an average number for each component under analysis. With FT-NIR, however, minimal sample preparation is needed and a single spectrum can be obtained in less than a minute ? fast enough, not just for cheese processing, but also for the control of many other processes requiring the correct blending of raw materials.
Another supplier of NIR and FT-NIR technology to the food and dairy industry is the Danish company Q-Interline, whose products are distributed in the UK through QuadraChem Laboratories. According to product manager Mark Whatten, Q-Interline's analysers ? based on proven ABB Bomem FT-NIR technology ? have a wide range of applications in the dairy sector. "The cost-sensitive balance between moisture and fat content can quickly be determined for products such as processed cheese, butter, margarines, spreads, whey protein concentrate, milk powder and many other products," he says.
Although most of these instruments are for at-line or laboratory use, many are also available in on-line versions, allowing fully automated analysis directly in the process. This is facilitated by an innovative on-line cell that Q-Interline has developed for use in the pipe.
With no glass or sapphire parts contacting the foodstuff, the Tefwin Dairy NIR on-line cell is said to be the only cell built entirely of food-grade materials. Light is transmitted to and received from the Tefwin cell via a 2mm fibre optic cable, which is a similar method to that used by the FOP-38 on-line analyser introduced last year by NIR Technology Australia.
With this system a remote sampling device is mounted in the process either in a solids handling auger, a pipe or a conveyor belt. The fibre optic cable connects the sampler to the NIR spectrometer that can be positioned up to 10m away from the sampling point.
Microbial spoilage
Closer to home in the UK, a research team at the University of Manchester has been using FTIR spectroscopy to develop a rapid detection method for microbial spoilage in food before it leaves the production process (see Food Manufacture, October 2005, p38). Successfully tested on chicken and beef, but still at the "proof of concept" stage according to the team leader Professor Roy Goodacre of the Department of Chemistry, this technique combines FTIR spectroscopy of the sample surface, in situ in the process, with a data handling process known as machine learning. "We have been able to acquire a metabolic snapshot and quantify, non-invasively, the microbial loads of food samples accurately and rapidly in 60 seconds, directly from the sample surface," says Goodacre.
However, despite the growing number of food applications of FTIR and NIR spectroscopy, there remains much to be said for the more traditional techniques of wet chemistry. This is certainly the view of Clive Grantham, md of lab equipment supplier Metrohm UK. "FTIR and NIR are all well and good," he says, "but each product needs repeated calibration. The techniques are not quite the utopia many were expecting, and often traditional methods such as titration and ISE [ion selective electrodes] are the best."
Metrohm has lab-based versions of these standard analytical techniques and has just taken on the distributorship for the on-line analysers of the Dutch company Applikon. Offering the generic methods of titration, ISE measurements and colorimetry, the Applikon analysers are situated close to process sampling points and can be used to determine parameters such as acidity, ascorbic acid content, chloride, citric and fatty acids, glucose, lactic acid and sulphites.
Whether it's traditional wet chemistry or the more esoteric sensor projects of universities, the attractions of on-line analysis seem to be catching on: a trend likely to accelerate if the general picture painted by Grantham is anything to go by.
"Technical skill levels in general are dropping in laboratories, especially in the food sector where short-term contract work is not uncommon," he says. All the more reason for taking the lab on-line wherever possible. FM
KEY CONTACTS
- Food Sensor Network 01372 376761
- GoodFood Project 0034 935 947700
- Metrohm UK 01280 824824
- NIR Technology Australia 0061 29708 5068
- Oxford Instruments 01865 393200
- QuadraChem Laboratories 01342 820828
- Thermo Electron 01788 820300
- University of Manchester 0161 306 4480